Method for Manufacturing Display Device and Method for Manufacturing Electronic Device

ABSTRACT

A method for manufacturing a display device is provided. The method includes: forming, between a first substrate and a second substrate, a light-emitting element including an electroluminescence layer and a wiring over which a peeling layer formed by using the material of the electroluminescence layer is provided; and peeling whole of the second substrate from the first substrate so that the peeling layer over the wiring is simultaneously exposed.

This application is a continuation of copending U.S. application Ser.No. 14/644,749, filed on Mar. 11, 2015 which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device. The present inventionalso relates to a method for manufacturing the display device.

Note that one embodiment of the present invention is not limited to theabove technical field.

Note that in this specification and the like, a semiconductor devicegenerally means a device that can function by utilizing semiconductorcharacteristics. Thus, a semiconductor element such as a transistor or adiode and a semiconductor circuit are semiconductor devices. A displaydevice, a light-emitting device, a lighting device, an electro-opticaldevice, an electronic device, and the like may include a semiconductorelement or a semiconductor circuit. Therefore, a display device, alight-emitting device, a lighting device, an electro-optical device, anelectronic device, and the like include a semiconductor device in somecases.

2. Description of the Related Art

In recent years, research and development have been extensivelyconducted on liquid crystal elements as a display element used in adisplay region of a display device. In addition, research anddevelopment have been extensively conducted on light-emitting elementsutilizing electroluminescence (EL). As a basic structure of theselight-emitting elements, a layer containing a light-emitting substanceis provided between a pair of electrodes. Voltage is applied to thislight-emitting element to obtain light emission from the light-emittingsubstance.

Light-emitting elements are a self-luminous element; thus, a displaydevice using the light-emitting elements has, in particular, advantagessuch as high visibility, no necessity of a backlight, and low powerconsumption. The display device using the light-emitting elements alsohas advantages in that it can be manufactured to be thin and lightweightand has high response speed.

A display device including the display elements can have flexibility;therefore, the use of a flexible substrate for the display device hasbeen proposed.

As a method for manufacturing a display device using a flexiblesubstrate, a technique has been developed in which an oxide layer and ametal layer are formed between a substrate and a semiconductor element,the substrate is separated by utilizing weak adhesion of an interfacebetween the oxide layer and the metal layer, and then the semiconductorelement is transferred to another substrate (e.g., a flexible substrate)(Patent Document 1).

In some cases, over a light-emitting element that has been formed over aflexible substrate, another flexible substrate is provided in order toprotect a surface of the light-emitting element or prevent entry ofmoisture or impurities from the outside.

[Patent Document 1] Japanese Published Patent Application No.2003-174153 SUMMARY OF THE INVENTION

In order to supply a signal or electric power to a display device usinga flexible substrate, it is necessary that part of the flexiblesubstrate be removed by a laser beam or an edged tool to expose anelectrode so that an external electrode such as a flexible printedcircuit (FPC) is connected to the electrode.

However, a method in which part of a flexible substrate is removed by alaser beam or with an edged tool has a problem in that an electrodeincluded in a display device is damaged easily and the reliability andmanufacturing yield of the display device are reduced easily. Inaddition, a display region and an electrode need to be provided with asufficient space therebetween in order to prevent damage to the displayregion due to the above-described method; for this reason, signalattenuation, electric power attenuation, or the like due to an increasein wiring resistance is caused easily.

An object of one embodiment of the present invention is to provide amethod for manufacturing a display device, which does not easily damagean electrode. Another object of one embodiment of the present inventionis to provide a method for manufacturing a display device, which doesnot easily damage a display region. Another object of one embodiment ofthe present invention is to provide a highly reliable display device anda method for manufacturing the display device.

Another object of one embodiment of the present invention is to providea display device, electronic device, or the like having high visibility.Another object of one embodiment of the present invention is to providea display device, electronic device, or the like having high displayquality. Another object of one embodiment of the present invention is toprovide a display device, electronic device, or the like having highreliability. Another object of one embodiment of the present inventionis to provide a display device, electronic device, or the like that isunlikely to be broken. Another object of one embodiment of the presentinvention is to provide a display device, electronic device, or the likewith low power consumption.

Note that the descriptions of these objects do not disturb the existenceof other objects. In one embodiment of the present invention, there isno need to achieve all of these objects. Other objects will be apparentfrom and can be derived from the description of the specification, thedrawings, the claims, and the like.

According to one embodiment of the present invention, a method formanufacturing a display device include a first process, a secondprocess, a third process, a fourth process, a fifth process, a sixthprocess, and a seventh process. The first process includes a step ofproviding a first layer over a first surface of a first substrate, astep of providing a first insulating layer over the first layer, a stepof providing an electrode over the first insulating layer, a step ofproviding a second insulating layer over the electrode, a step ofproviding a first opening by partly removing the second insulatinglayer, and a step of providing a display element and a second layer overthe second insulating layer. The second process includes a step ofproviding a third layer over a second surface of a second substrate, astep of providing a third insulating layer over the third layer, and astep of providing a second opening by partly removing the third layerand the third insulating layer. The third process includes a step ofoverlapping the first substrate and the second substrate with each otherwith a bonding layer provided therebetween so that a region in which thefirst surface and the second surface face each other and in which thefirst opening and the second opening overlap with each other is formed.The fourth process includes a step of peeling the first substrate fromthe first insulating layer together with the first layer. The fifthprocess includes a step of providing a third substrate so as to overlapwith the first insulating layer. The sixth process includes a step ofpeeling the second substrate from the third insulating layer togetherwith the third layer. The seventh process includes a step of providing afourth substrate so as to overlap with the third insulating layer. Inthe first process, the electrode and the second layer are provided atleast partly in contact with each other. In the third process, thebonding layer includes a first region in which the bonding layer and thesecond opening overlap with each other, and the second layer includes asecond region in which the second layer and the second opening overlapwith each other. In the sixth process, at least part of the bondinglayer in the first region and at least part of the second layer in thesecond region are peeled together with the second substrate so that partof the electrode is exposed.

One embodiment of the present invention provides a method formanufacturing a display device, which does not easily damage anelectrode. One embodiment of the present invention provides a method formanufacturing a display device, which does not easily damage a displayregion. One embodiment of the present invention provides a highlyreliable display device and a method for manufacturing the displaydevice.

One embodiment of the present invention provides a display device,electronic device, or the like having high visibility. One embodiment ofthe present invention provides a display device, electronic device, orthe like having high display quality. One embodiment of the presentinvention provides a display device, electronic device, or the likehaving high reliability. One embodiment of the present inventionprovides a display device, electronic device, or the like that isunlikely to be broken. One embodiment of the present invention providesa display device, electronic device, or the like with low powerconsumption.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot necessarily have all of these effects. Other effects will beapparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are a perspective view and a cross-sectional viewillustrating one embodiment of a display device.

FIGS. 2A and 2B are a perspective view and a cross-sectional viewillustrating one embodiment of a display device.

FIGS. 3A and 3B are cross-sectional views each illustrating oneembodiment of a display device.

FIGS. 4A to 4E illustrate a manufacturing process of one embodiment of adisplay device.

FIGS. 5A to 5D illustrate a manufacturing process of one embodiment of adisplay device.

FIGS. 6A to 6F illustrate a manufacturing process of one embodiment of adisplay device.

FIGS. 7A to 7C each illustrate an example of a pixel configuration ofone embodiment of a display device.

FIGS. 8A and 8B illustrate a manufacturing process of one embodiment ofa display device.

FIGS. 9A and 9B illustrate a manufacturing process of one embodiment ofa display device.

FIGS. 10A and 10B illustrate a manufacturing process of one embodimentof a display device.

FIGS. 11A and 11B are a perspective view and a cross-sectional viewillustrating one embodiment of a display device.

FIGS. 12A and 12B are a perspective view and a cross-sectional viewillustrating one embodiment of a display device.

FIGS. 13A to 13C are each a cross-sectional view illustrating oneembodiment of a display device.

FIGS. 14A and 14B are a perspective view and a cross-sectional viewillustrating one embodiment of a display device.

FIGS. 15A and 15B are cross-sectional views illustrating one embodimentof a display device.

FIG. 16 is a cross-sectional view illustrating one embodiment of adisplay device.

FIGS. 17A to 17C are a block diagram and circuit diagrams illustratingone embodiment of a display device.

FIGS. 18A1, 18A2, 18B1, and 18B2 are each a cross-sectional view of oneembodiment of a transistor.

FIGS. 19A1, 19A2, 19A3, 19B1, and 19B2 are each a cross-sectional viewillustrating one embodiment of a transistor.

FIGS. 20A and 20B illustrate structure examples of a light-emittingelement.

FIG. 21 illustrates a display module.

FIGS. 22A to 22E illustrate examples of electronic devices and lightingdevices.

FIGS. 23A and 23B illustrate an example of an electronic device.

FIGS. 24A to 24C illustrate an example of an electronic device.

FIGS. 25A to 25C are a plan view and cross-sectional views illustratingan example of an electronic device.

FIGS. 26A and 26B are perspective views illustrating an example of anelectronic device.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail with reference to theaccompanying drawings. Note that the present invention is not limited tothe description below, and it is understood easily by those skilled inthe art that various changes and modifications can be made withoutdeparting from the spirit and scope of the present invention. Therefore,the present invention should not be construed as being limited to thedescription in the following embodiments. In the structures of thepresent invention to be described below, the same portions or portionshaving similar functions are denoted by the same reference numerals indifferent drawings, and explanation thereof will not be repeated.

The position, size, range, and the like of each component illustrated inthe drawings and the like are not accurately represented in some casesto facilitate understanding of the invention. Therefore, the disclosedinvention is not necessarily limited to the position, the size, range,and the like disclosed in the drawings and the like. For example, in theactual manufacturing process, a resist mask or the like might beunintentionally reduced in size by treatment such as etching, whichmight not be illustrated for easy understanding.

Especially in a top view (also referred to as a plan view), somecomponents might not be illustrated for easy understanding.

In this specification and the like, the term such as an “electrode” or a“wiring” does not limit a function of a component. For example, an“electrode” is used as part of a “wiring” in some cases, and vice versa.Furthermore, the tem). “electrode” or “wiring” can also mean acombination of a plurality of “electrodes” and “wirings” formed in anintegrated manner.

Note that the term “over” or “under” in this specification and the likedoes not necessarily mean that a component is placed “directly on” or“directly below” and “directly in contact with” another component. Forexample, the expression “electrode B over insulating layer A” does notnecessarily mean that the electrode B is on and in direct contact withthe insulating layer A and can mean the case where another component isprovided between the insulating layer A and the electrode B.

Functions of a source and a drain might be switched depending onoperation conditions, for example, when a transistor having oppositepolarity is employed or the direction of current flow is changed incircuit operation. Thus, it is difficult to define which is a source ora drain. Accordingly, the terms “source” and “drain” can be switched inthis specification.

Note that in this specification and the like, the expression“electrically connected” includes the case where components areconnected through an “object having any electric function”. There is noparticular limitation on an “object having any electric function” aslong as electric signals can be transmitted and received betweencomponents that are connected through the object. Accordingly, even whenthe expression “electrically connected” is used in this specification,there is a case in which no physical connection is made and a wiring isjust extended in an actual circuit.

In this specification, a term “parallel” indicates that the angle formedbetween two straight lines is greater than or equal to −10° and lessthan or equal to 10°, and accordingly also includes the case where theangle is greater than or equal to −5° and less than or equal to 5°. Aterm “perpendicular” indicates that the angle formed between twostraight lines is greater than or equal to 80° and less than or equal to100°, and accordingly also includes the case where the angle is greaterthan or equal to 85° and less than or equal to 95°.

In this specification, in the case where an etching step is performedafter a lithography process, a resist mask formed in the lithographyprocess is removed after the etching step, unless otherwise specified.

A voltage usually refers to a potential difference between a givenpotential and a reference potential (e.g., a ground potential (a GNDpotential) or a source potential). A voltage can be referred to as apotential and vice versa.

Note that an impurity in a semiconductor refers to, for example,elements other than the main components of the semiconductor. Forexample, an element with a concentration lower than 0.1 atomic % can beregarded as an impurity. When an impurity is contained, the density ofstates (DOS) in a semiconductor may be increased, the carrier mobilitymay be decreased, or the crystallinity may be decreased, for example. Inthe case where the semiconductor is an oxide semiconductor, examples ofan impurity which changes characteristics of the semiconductor includeGroup 1 elements, Group 2 elements, Group 13 elements, Group 14elements, Group 15 elements, and transition metals other than the maincomponents of the oxide semiconductor; specifically, there are hydrogen(included in water), lithium, sodium, silicon, boron, phosphorus,carbon, and nitrogen, for example. In the case of an oxidesemiconductor, oxygen vacancies may be formed by entry of impuritiessuch as hydrogen. In the case where the semiconductor is silicon,examples of an impurity which changes characteristics of thesemiconductor include oxygen, Group 1 elements except hydrogen, Group 2elements, Group 13 elements, and Group 15 elements.

Note that ordinal numbers such as “first” and “second” in thisspecification and the like are used in order to avoid confusion amongcomponents and do not denote the priority or the order such as the orderof steps or the stacking order. A term without an ordinal number in thisspecification and the like might be provided with an ordinal number in aclaim in order to avoid confusion among components. A term with anordinal number in this specification and the like might be provided witha different ordinal number in a claim. Moreover, a term with an ordinalnumber in this specification and the like might not be provided with anyordinal number in a claim.

Note that in this specification, the channel length refers to, forexample, a distance, observed in a top view of a transistor, between asource (a source region or a source electrode) and a drain (a drainregion or a drain electrode) in a region where a semiconductor (or aportion where a current flows in a semiconductor when the transistor ison) and a gate electrode overlap with each other or a region where achannel is formed. In one transistor, channel lengths are notnecessarily the same in all regions. In other words, the channel lengthof one transistor is not limited to one value in some cases. Therefore,in this specification, the channel length is any one of values, themaximum value, the minimum value, or the average value in a region wherea channel is formed.

The channel width refers to, for example, the length of a portion wherea source and a drain face each other in a region where a semiconductor(or a portion where a current flows in a semiconductor when a transistoris on) and a gate electrode overlap with each other, or a region where achannel is formed. In one transistor, channel widths are not necessarilythe same in all regions. In other words, the channel width of onetransistor is not limited to one value in some cases. Therefore, in thisspecification, a channel width is any one of values, the maximum value,the minimum value, or the average value in a region where a channel isformed.

Embodiment 1

A structure example of a display device 100 of one embodiment of thepresent invention will be described with reference to FIGS. 1A and 1B,FIGS. 2A and 2B, FIGS. 3A and 3B, FIGS. 4A to 4E, FIGS. 5A to 5D, FIGS.6A to 6F, FIGS. 7A to 7C, FIGS. 8A and 8B, FIGS. 9A and 9B, FIGS. 10Aand 10B, FIGS. 11A and 11B, and FIGS. 12A and 12B. FIG. 1A is aperspective view of the display device 100 to which an externalelectrode 124 is connected, and FIG. 1B is a cross-sectional view takenalong the dashed-dotted line A1-A2 in FIG. 1A. Note that the displaydevice 100 disclosed in this specification is a display device in whicha light-emitting element is used as a display element. As the displaydevice 100 of one embodiment of the present invention, a display devicehaving a top-emission structure is described as an example. Note thatthe display device 100 can be a display device having a bottom-emissionstructure or a dual-emission structure.

<Structure of Display Device>

The display device 100 described in this embodiment includes a displayregion 131. The display region 131 includes a plurality of pixels 130.One pixel 130 includes at least one light-emitting element 125.

The display device 100 described in this embodiment includes anelectrode 115, an EL layer 117, an electrode 118, a partition 114, andan electrode 116. The display device 100 further includes an insulatinglayer 141 over the electrode 116, and the electrode 115 and theelectrode 116 are electrically connected to each other in an opening 128provided in the insulating layer 141. The partition 114 is provided overthe electrode 115, the EL layer 117 is provided over the electrode 115and the partition 114, and the electrode 118 is provided over the ELlayer 117.

The light-emitting element 125 is provided over a substrate 111 with abonding layer 112, an insulating layer 119, and the insulating layer 141provided therebetween. The light-emitting element 125 includes theelectrode 115, the EL layer 117, and the electrode 118.

The display device 100 described in this embodiment includes a substrate121 provided over the electrode 118 with a bonding layer 120 providedtherebetween. In addition, the substrate 121 is provided with alight-blocking layer 264, a coloring layer (also referred to as a colorfilter) 266, and an overcoat layer 268 with a bonding layer 122 and aninsulating layer 129 provided therebetween.

Since the display device 100 described in this embodiment has atop-emission structure, light 151 emitted from the EL layer 117 isextracted from the substrate 121 side. The light 151 (e.g., white light)emitted from the EL layer 117 is partly absorbed when transmittedthrough the coloring layer 266 and converted into light with a specificcolor. In other words, the coloring layer 266 transmits light with aspecific wavelength range. The coloring layer 266 can function as anoptical filter layer for converting the light 151 into light of adifferent color.

Although the electrode 116 has a single-layer structure in thisembodiment, the electrode 116 may have a stacked-layer structure of twoor more layers.

Each of the substrate 121, the bonding layer 122, the insulating layer129, the bonding layer 120, and the insulating layer 141 has an opening.The openings occupy regions which overlap with one another and eachoverlap with the electrode 116. In this specification and the like,these openings are collectively referred to as an opening 132. In theopening 132, the external electrode 124 and the electrode 116 areelectrically connected to each other through an anisotropic conductiveconnection layer 138.

Note that as illustrated in FIGS. 2A and 2B, it is possible not toprovide the light-blocking layer 264, the coloring layer 266, and theovercoat layer 268 in the display device 100. FIG. 2A is a perspectiveview of the display device 100 in which the light-blocking layer 264,the coloring layer 266, and the overcoat layer 268 are not provided, andFIG. 2B is a cross-sectional view taken along the dashed-dotted lineA3-A4 in FIG. 2A.

In particular, in the case where the EL layer 117 is provided by what iscalled side-by-side patterning in which the colors of the lights 151emitted from different pixels are different, the coloring layer 266 maybe provided or is not necessarily provided.

When at least one or all of the light-blocking layer 264, the coloringlayer 266, and the overcoat layer 268 are not provided, the displaydevice 100 can achieve a reduction in manufacturing cost, yieldimprovement, or the like. Moreover, the light 151 can be emittedefficiently when the coloring layer 266 is not provided; therefore,luminance can be improved or power consumption can be reduced, forexample.

On the other hand, when the light-blocking layer 264, the coloring layer266, and the overcoat layer 268 are provided, reflection of externallight is suppressed and thus a contrast ratio, color reproducibility, orthe like can be improved.

Note that in the case where the display device 100 has a bottom-emissionstructure, the light-blocking layer 264, the coloring layer 266, and theovercoat layer 268 may be provided on the substrate 111 side (see FIG.3A). In the case where the display device 100 has a dual-emissionstructure, the light-blocking layer 264, the coloring layer 266, and theovercoat layer 268 may be provided on either or both of the substrate111 side and the substrate 121 side (see FIG. 3B).

A switching element having a function of supplying a signal to thelight-emitting element 125 may be provided between the light-emittingelement 125 and the electrode 116. For example, a transistor may beprovided between the light-emitting element 125 and the electrode 116.

A transistor is a kind of semiconductor element and enablesamplification of current and/or voltage, switching operation forcontrolling conduction or non-conduction, or the like. By providing atransistor between the light-emitting element 125 and the electrode 116,an increase in the area of the display region 131 and ahigher-resolution display can be achieved easily. Note that a resistor,an inductor, a capacitor, a rectifier element, or the like, withoutlimitation to a switching element such as a transistor, can be providedin the display region 131.

[Substrates 111 and 121]

An organic resin material, a glass material that is thin enough to haveflexibility, or the like can be used for the substrate 111 and thesubstrate 121. In the case where the display device 100 has abottom-emission structure or a dual-emission structure, a materialhaving a light-transmitting property with respect to light emitted fromthe EL layer 117 is used for the substrate 111. In the case where thedisplay device 100 has a top-emission structure or a dual-emissionstructure, a material having a light-transmitting property with respectto light emitted from the EL layer 117 is used for the substrate 121.

As a material that has flexibility and transmits visible light, whichcan be used for the substrate 111 and the substrate 121, the followingcan be used: a poly(ethylene terephthalate) resin (PET), a poly(ethylenenaphthalate) resin (PEN), a poly(ether sulfone) resin (PES), apolyacrylonitrile resin, an acrylic resin, a polyimide resin, apoly(methyl methacrylate) resin, a polycarbonate resin, a polyamideresin, a polycycloolefin resin, a polystyrene resin, a poly(amide imide)resin, a polypropylene resin, a polyester resin, a poly(vinyl halide)resin, an aramid resin, an epoxy resin, or the like. Alternatively, amixture or a stack including any of these materials may be used. Notethat the same material or different materials may be used for thesubstrate 111 and the substrate 121.

The thermal expansion coefficients of the substrate 121 and thesubstrate 111 are preferably less than or equal to 30 ppm/K, or furtherpreferably less than or equal to 10 ppm/K. On surfaces of the substrate121 and the substrate 111, a protective film having low waterpermeability may be formed; examples of the protective film include afilm containing nitrogen and silicon such as a silicon nitride film or asilicon oxynitride film and a film containing nitrogen and aluminum suchas an aluminum nitride film. Note that a structure in which a fibrousbody is impregnated with an organic resin (also called prepreg) may beused as the substrate 121 and the substrate 111.

[Insulating Layer 119]

The insulating layer 119 can be formed to have a single-layer structureor a multi-layer structure using an oxide material such as aluminumoxide, magnesium oxide, silicon oxide, silicon oxynitride, galliumoxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide,neodymium oxide, hafnium oxide, or tantalum oxide; a nitride materialsuch as silicon nitride, silicon nitride oxide, aluminum nitride, oraluminum nitride oxide; or the like. The insulating layer 119 may have,for example, a two-layer structure of silicon oxide and silicon nitrideor a five-layer structure in which materials selected from the above arecombined. The insulating layer 119 can be formed by a sputtering method,a CVD method, a thermal oxidation method, a coating method, a printingmethod, or the like.

The insulating layer 119 can prevent or reduce diffusion of an impurityelement from the substrate 111, the bonding layer 112, or the like tothe light-emitting element 125.

Note that in this specification, a nitride oxide refers to a compoundthat contains more nitrogen than oxygen. An oxynitride refers to acompound that contains more oxygen than nitrogen. The content of eachelement can be measured by Rutherford backscattering spectrometry (RBS),for example.

[Electrode 116]

The electrode 116 can be formed using a conductive material. Forexample, a metal element selected from aluminum, chromium, copper,silver, gold, platinum, tantalum, nickel, titanium, molybdenum,tungsten, hafnium, vanadium, niobium, manganese, magnesium, zirconium,beryllium, and the like; an alloy containing any of the above metalelements; an alloy containing a combination of the above metal elements;or the like can be used. A semiconductor typified by polycrystallinesilicon containing an impurity element such as phosphorus, or silicidesuch as nickel silicide may also be used. There is no particularlimitation on the formation method of the conductive material, and avariety of formation methods such as an evaporation method, a CVDmethod, a sputtering method, and a spin coating method can be employed.

The electrode 116 can also be formed using a conductive materialcontaining oxygen, such as indium tin oxide, indium oxide containingtungsten oxide, indium zinc oxide containing tungsten oxide, indiumoxide containing titanium oxide, indium tin oxide containing titaniumoxide, indium zinc oxide, or indium tin oxide to which silicon oxide isadded. Moreover, a conductive material containing nitrogen, such astitanium nitride, tantalum nitride, or tungsten nitride, can be used. Itis also possible to use a stacked-layer structure formed using the aboveconductive material containing oxygen and a material containing theabove metal element.

The electrode 116 may have a single-layer structure or a stacked-layerstructure of two or more layers. For example, a single-layer structureof an aluminum layer containing silicon, a two-layer structure in whicha titanium layer is stacked over an aluminum layer, a two-layerstructure in which a titanium layer is stacked over a titanium nitridelayer, a two-layer structure in which a tungsten layer is stacked over atitanium nitride layer, a two-layer structure in which a tungsten layeris stacked over a tantalum nitride layer, and a three-layer structure inwhich a titanium layer, an aluminum layer, and a titanium layer arestacked in this order are given. Alternatively, an aluminum alloycontaining one or more elements selected from titanium, tantalum,tungsten, molybdenum, chromium, neodymium, and scandium may be used asthe electrode 116.

[Insulating Layer 141]

The insulating layer 141 can be formed using a material and a methodthat are similar to those of the insulating layer 119. For theinsulating layer 141, a material containing oxygen is preferably used.

[Electrode 115]

The electrode 115 is preferably formed using a conductive material thatefficiently reflects light emitted from the EL layer 117 formed later.Note that the electrode 115 may have a stacked-layer structure of aplurality of layers without limitation to a single-layer structure. Forexample, in the case where the electrode 115 is used as an anode, alayer in contact with the EL layer 117 may be a light-transmittinglayer, such as an indium tin oxide layer, and a layer having highreflectance (e.g., aluminum, an alloy containing aluminum, or silver)may be provided in contact with the layer.

The display device having a top-emission structure is described as anexample in this embodiment. In the case of a display device having abottom-emission structure or a dual-emission structure, the electrode115 may be formed using a light-transmitting conductive material.

[Partition 114]

The partition 114 is provided in order to prevent an electrical shortcircuit between the adjacent electrodes 118. In the case of using ametal mask for formation of the EL layer 117 described later, thepartition 114 has a function of preventing the contact of metal maskwith a region where the light-emitting element 125 is formed. Thepartition 114 can be formed of an organic resin material such as anepoxy resin, an acrylic resin, or an imide resin or an inorganicmaterial such as silicon oxide. The partition 114 is preferably formedso that its sidewall has a tapered shape or a tilted surface with acontinuous curvature. The sidewall of the partition 114 having theabove-described shape enables favorable coverage with the EL layer 117and the electrode 118 formed later.

[EL Layer 117]

A structure of the EL layer 117 is described in Embodiment 5.

[Electrode 118]

The electrode 118 is used as a cathode in this embodiment, and thus theelectrode 118 is preferably formed using a material that has a low workfunction and can inject electrons into the EL layer 117 described later.As well as a single-layer of a metal having a low work function, a stackin which a metal material such as aluminum, a conductive oxide materialsuch as indium tin oxide, or a semiconductor material is formed over aseveral-nanometer-thick buffer layer formed of an alkali metal or analkaline earth metal having a low work function may be used as theelectrode 118. As the buffer layer, an oxide of an alkaline earth metal,a halide, a magnesium-silver, or the like can also be used.

In the case where light emitted from the EL layer 117 is extractedthrough the electrode 118, the electrode 118 preferably has a propertyof transmitting visible light.

[Bonding Layers 120, 112, and 122]

A light curable adhesive, a reaction curable adhesive, a thermosettingadhesive, or an anaerobic adhesive can be used as the bonding layer 120,the bonding layer 112, and the bonding layer 122. For example, an epoxyresin, an acrylic resin, or an imide resin can be used. A drying agent(e.g., zeolite) having a size less than or equal to the wavelength oflight emitted from the EL layer 117 or a filler (e.g., titanium oxide orzirconium) with a high refractive index is preferably mixed into thebonding layer 120 in the case of a top-emission structure or into thebonding layer 112 in the case of a bottom-emission structure, in whichcase the light-coupling efficiency of extracting light emitted from theEL layer 117 negligibly decrease and the reliability of the displaydevice is improved.

[Anisotropic Conductive Connection Layer 138]

The anisotropic conductive connection layer 138 can be formed using anyof various kinds of anisotropic conductive films (ACF), anisotropicconductive pastes (ACP), and the like.

The anisotropic conductive connection layer 138 is formed by curing apaste-form or sheet-form material that is obtained by mixing conductiveparticles to a thermosetting resin or a thermosetting and light curableresin. The anisotropic conductive connection layer 138 exhibits ananisotropic conductive property by light irradiation orthermocompression bonding. As the conductive particles used for theanisotropic conductive connection layer 138, for example, particles of aspherical organic resin coated with a thin-film metal such as Au, Ni, orCo can be used.

<Method for Manufacturing Display Device>

Next, a method for manufacturing the display device 100 is describedwith reference to FIGS. 4A to 4E, FIGS. 5A to 5D, FIGS. 6A to 6F, FIGS.7A to 7C, FIGS. 8A and 8B, FIGS. 9A and 9B, and FIGS. 10A and 10B. FIGS.4A to 10B other than FIGS. 7A to 7C are cross-sectional views takenalong the dashed-dotted line A1-A2 in FIGS. 1A and 1B.

[Formation of Peeling Layer 113]

First, a peeling layer 113 is formed over a substrate 101 (see FIG. 4A).The substrate 101 may be exemplified by a semiconductor substrate (e.g.,a single crystal substrate or a silicon substrate), an SOI substrate, aglass substrate, a quartz substrate, a sapphire substrate, a ceramicsubstrate, a plastic substrate which has heat resistance to theprocessing temperature in this embodiment, a metal substrate, astainless steel substrate, a substrate including stainless steel foil, atungsten substrate, and a substrate including tungsten foil. As anexample of a glass substrate, a barium borosilicate glass substrate, analuminoborosilicate glass substrate, and soda lime glass substrate canbe given.

The peeling layer 113 can be formed using an element selected fromtungsten, molybdenum, titanium, tantalum, niobium, nickel, cobalt,zirconium, ruthenium, rhodium, palladium, osmium, iridium, and silicon;an alloy material containing any of the elements; or a compound materialcontaining any of the elements. The peeling layer 113 can also be formedto have a single-layer structure or a stacked-layer structure using anyof the materials. Note that the crystalline structure of the peelinglayer 113 may be amorphous, microcrystalline, or polycrystalline. Thepeeling layer 113 can also be formed using a metal oxide such asaluminum oxide, gallium oxide, zinc oxide, titanium dioxide, indiumoxide, indium tin oxide, indium zinc oxide, or an oxide includingindium, gallium, and zinc (In—Ga—Zn—O, IGZO).

The peeling layer 113 can be formed by a sputtering method, a CVDmethod, a coating method, a printing method, or the like. Note that thecoating method includes a spin coating method, a droplet dischargemethod, and a dispensing method.

In the case where the peeling layer 113 has a single-layer structure,the peeling layer 113 is preferably formed using tungsten, molybdenum,or a material containing tungsten and molybdenum. Alternatively, thepeeling layer 113 is preferably formed using an oxide or oxynitride oftungsten, an oxide or oxynitride of molybdenum, or an oxide oroxynitride of an alloy material containing tungsten and molybdenum.

In the case where the peeling layer 113 has a stacked-layer structureincluding, for example, a layer containing tungsten and a layercontaining an oxide of tungsten, the layer containing an oxide oftungsten may be formed as follows: the layer containing tungsten isformed first and then an insulating oxide layer is formed in contacttherewith, so that the layer containing an oxide of tungsten is formedat the interface between the layer containing tungsten and theinsulating oxide layer. Alternatively, the layer containing an oxide oftungsten may be formed by performing thermal oxidation treatment, oxygenplasma treatment, treatment with an oxidizing solution such as ozonewater, or the like on the surface of the layer containing tungsten.Moreover, an insulating layer may be provided between the substrate 101and the peeling layer 113.

In this embodiment, aluminoborosilicate glass is used for the substrate101. As the peeling layer 113, a tungsten film is formed over thesubstrate 101 by a sputtering method.

[Formation of Insulating Layer 119]

Next, the insulating layer 119 is formed over the peeling layer 113 (seeFIG. 4A). The insulating layer 119 can prevent or reduce diffusion of animpurity element from the substrate 101 or the like. After the substrate101 is replaced with the substrate 111, the insulating layer 119 canprevent or reduce diffusion of an impurity element from the substrate111, the bonding layer 112, or the like to the light-emitting element125. The thickness of the insulating layer 119 is preferably greaterthan or equal to 30 nm and less than or equal to 2 μm, furtherpreferably greater than or equal to 50 nm and less than or equal to 1 orstill further preferably greater than or equal to 50 nm and less than orequal to 500 nm. In this embodiment, the insulating layer 119 is formedby stacking a 600-nm-thick silicon oxynitride film, a 200-nm-thicksilicon nitride film, a 200-nm-thick silicon oxynitride film, a140-nm-thick silicon nitride oxide film, and a 100-nm-thick siliconoxynitride film by a plasma CVD method from the substrate 101 side.

Note that it is preferable to expose the surface of the peeling layer113 to an atmosphere containing oxygen before the formation of theinsulating layer 119.

As the gas used in the atmosphere containing oxygen, oxygen, dinitrogenmonoxide, nitrogen dioxide, carbon dioxide, carbon monoxide, or the likecan be used. A mixed gas of a gas containing oxygen and another gas maybe used. For example, a mixed gas of a gas containing oxygen and a raregas, for example, a mixed gas of carbon dioxide and argon may be used.Oxidizing the surface of the peeling layer 113 can facilitate peeling ofthe substrate 101 performed later.

[Formation of Electrode 116]

Next, a conductive layer 126 for forming the electrode 116 is formedover the insulating layer 119. As the conductive layer 126, athree-layer metal film in which a layer of aluminum is provided betweentwo layers of molybdenum is formed over the insulating layer 119 by asputtering method, for example (see FIG. 4A).

After that, a resist mask is formed over the conductive layer 126, andthe conductive layer 126 is etched into a desired shape using the resistmask. In the above-described manner, the electrode 116 is formed. Theresist mask can be formed by a lithography method, a printing method, aninkjet method, or the like as appropriate. Formation of the resist maskby an inkjet method needs no photomask; thus, manufacturing cost can bereduced.

The etching of the conductive layer 126 may be performed by a dryetching method, a wet etching method, or both of them. In the case wherethe conductive layer 126 is etched by a wet etching method, a solutionobtained by mixing phosphoric acid, acetic acid, and nitric acid, asolution containing oxalic acid, a solution containing phosphoric acid,or the like can be used as an etchant. After the etching treatment, theresist mask is removed (see FIG. 4B).

When the electrode 116 (including other electrodes and wirings formedusing the same layer) has a taper-shaped end portion, the coverage witha layer that covers the side surfaces of the electrode 116 can beimproved. Specifically, the end portion has a taper angle θ of 80° orless, preferably 60° or less, or further preferably 45° or less. Notethat the “taper angle” refers to an inclination angle formed by a sidesurface and a bottom surface. The shape of an end portion having a taperangle smaller than 90° is called a forward tapered shape, and the shapeof an end portion having a taper angle larger than or equal to 90° iscalled an inverse tapered shape. FIG. 4B illustrates the case where theend portion of the electrode 116 has a forward tapered shape.

Alternatively, the cross-sectional shape of the end portion of theelectrode 116 has a plurality of steps, so that the coverage with thelayer formed thereon can be improved. The above description is notlimited to the electrode 116 and, when the end portion of each layer hasa forward taper shape or a step-like shape in a cross section, aphenomenon that a layer formed to cover the end portion is cut(disconnection) at the end portion can be prevented, so that thecoverage becomes favorable.

[Formation of Insulating Layer 127]

Next, an insulating layer 127 is formed over the electrode 116 (see FIG.4C). In this embodiment, a silicon oxynitride film is formed by a plasmaCVD method as the insulating layer 127.

Next, a resist mask is formed over the insulating layer 127, and part ofthe insulating layer 127 overlapping with the electrode 116 isselectively removed using the resist mask, so that the insulating layer141 having the opening 128 and an opening 137 is formed (see FIG. 4D).The etching of the insulating layer 127 may be performed by a dryetching method, a wet etching method, or both of them.

[Formation of Electrode 115]

Next, a conductive layer 145 for forming the electrode 115 is formedover the insulating layer 141 (see FIG. 4E). The conductive layer 145can be formed using a material and a method that are the same as thoseof the conductive layer 126 (electrode 116).

Next, a resist mask is formed over the conductive layer 145, and part ofthe conductive layer 145 is selectively removed using the resist mask,so that the electrode 115 is formed (see FIG. 5A). The etching of theconductive layer 145 may be performed by a dry etching method, a wetetching method, or both of them. In this embodiment, the conductivelayer 145 (electrode 115) is formed using a material in which indium tinoxide is stacked over silver. The electrode 115 and the electrode 116are electrically connected to each other through the opening 128.

[Formation of Partition 114]

Next, the partition 114 is formed (see FIG. 5B). In this embodiment, thepartition 114 is formed in such a manner that a photosensitive organicresin material is applied by a coating method and processed into adesired shape. In this embodiment, the partition 114 is formed using aphotosensitive polyimide resin.

[Formation of EL Layer 117, Electrode 118, and Peeling Layer 110]

In this embodiment, a peeling layer 110 having a two-layer structure ofa peeling layer 110 a formed using the same material as the EL layer 117and a peeling layer 110 b formed using the same material as theelectrode 118 is formed. Such a structure is preferable because thepeeling layer 110 can be formed without an increase in the number ofmanufacturing steps.

After the formation of the partition 114, the EL layer 117 is formedover the electrode 115 and the partition 114 and, at the same time, thepeeling layer 110 a is formed in a region over the electrode 116 whichoverlaps with the opening 137 (see FIG. 5C).

Next, the electrode 118 is formed over the EL layer 117 and, at the sametime, the peeling layer 110 b is formed over the peeling layer 110 a. Inthis embodiment, an alloy of magnesium and silver is used for theelectrode 118 and the peeling layer 110 b. The electrode 118 and thepeeling layer 110 b can be formed by an evaporation method, a sputteringmethod, or the like (see FIG. 5D).

Note that the peeling layer 110 formed in and on the opening 137 overthe electrode 116 may be formed to have a single-layer structure or astacked-layer structure of two or more layers. In the case where thepeeling layer 110 has a single-layer structure, the peeling layer 110can be formed using a material having low adhesion to the electrode 116.In the case where the peeling layer 110 has a stacked-layer structure, aplurality of materials can be used so that adhesion between layers inthe stack is decreased.

In this embodiment, a substrate 101 over which the light-emittingelement 125 is formed is referred to as an element substrate 171.

Next, a method for manufacturing a counter substrate 181 is described.

[Formation of Peeling Layer 143]

First, a peeling layer 143 is formed over a substrate 102 (see FIG. 6A).The substrate 102 can be formed using a material similar to that of thesubstrate 101. Note that the same material or different materials may beused for the substrate 101 and the substrate 102. The peeling layer 143can be formed in a manner similar to that of the peeling layer 113.Moreover, an insulating layer may be provided between the substrate 102and the peeling layer 143. In this embodiment, aluminoborosilicate glassis used for the substrate 102. As the peeling layer 143, a tungsten filmis formed over the substrate 102 by a sputtering method.

Note that it is preferable to expose the surface of the peeling layer143 to an atmosphere containing oxygen or a plasma atmosphere containingoxygen after the formation of the peeling layer 143. Oxidizing thesurface of the peeling layer 143 can facilitate peeling of the substrate102 performed later.

[Formation of Insulating Layer 149]

Next, an insulating layer 149 is formed over the peeling layer 143 (seeFIG. 6A). The insulating layer 149 can be formed using a material and amethod that are similar to those of the insulating layer 119. In thisembodiment, the insulating layer 149 is formed by stacking a200-nm-thick silicon oxynitride film, a 140-nm-thick silicon nitrideoxide film, and a 100-nm-thick silicon oxynitride film by a plasma CVDmethod from the substrate 102 side.

[Formation of Peeling Layer 123 and Insulating Layer 129]

Subsequently, a resist mask is formed over, the insulating layer 149,and part of the insulating layer 149 and part of the peeling layer 143are selectively removed using the resist mask, so that a peeling layer123 and the insulating layer 129 having an opening 139 are formed. Theresist mask can be formed by a lithography method, a printing method, aninkjet method, or the like as appropriate. Formation of the resist maskby an inkjet method needs no photomask; thus, manufacturing cost can bereduced.

The etching of the insulating layer 149 and the peeling layer 143 may beperformed by a dry etching method, a wet etching method, or both ofthem. After the etching treatment, the resist mask is removed (see FIG.6B).

[Formation of Light-Blocking Layer 264]

Next, a layer 274 for forming the light-blocking layer 264 is formedover the insulating layer 129 (see FIG. 6C). The layer 274 may have asingle-layer structure or a stacked-layer structure including two ormore layers. Examples of a material for the layer 274 are a metalmaterial including chromium, titanium, nickel, or the like; or an oxidematerial including chromium, titanium, nickel, or the like.

In the case where the layer 274 is formed using the metal material orthe oxide material, a resist mask is formed over the layer 274, and thelayer 274 is etched into a desired shape using the resist mask, so thatthe light-blocking layer 264 is formed (see FIG. 6D). With amacromolecular material in which carbon black is dispersed, directwriting of the light-blocking layer 264 can be performed over theinsulating layer 129 by an inkjet method.

[Formation of Coloring Layer 266]

Next, the coloring layer 266 is formed over the insulating layer 129(see FIG. 6E). Each coloring layer 266 is formed in a desired positionwith any of various materials by a printing method, an inkjet method, ora photolithography method. At this time, the coloring layer 266 ispreferably provided so as to partly overlap with the light-blockinglayer 264. Color display can be performed by providing the coloringlayers 266 of different colors in different pixels.

Here, examples of a pixel configuration for achieving color display aredescribed with reference to FIGS. 7A to 7C. FIGS. 7A to 7C are enlargedplan views of a region 170 in the display region 131 of FIG. 1A. Forexample, as illustrated in FIG. 7A, three pixels 130 arranged in astripe pattern function as subpixels and can be correctively used as onepixel 140. Full color display can be achieved in such a manner that thered, green, and blue coloring layers 266 are used so as to correspond tothree pixels 130. In FIG. 7A, the pixel 130 emitting red light, thepixel 130 emitting green light, and the pixel 130 emitting blue lightare illustrated as a pixel 130R, a pixel 130G, and a pixel 130B,respectively. Note that the colors of the coloring layers 266 may be acolor other than red, green, and blue; for example, the coloring layer266 may be yellow, cyan, magenta, or the like.

As illustrated in FIG. 7B, four pixels 130 may function as a subpixeland may be collectively used as one pixel 140. For example, the coloringlayers 266 corresponding to the four pixels 130 may be red, green, blue,and yellow. In FIG. 7B, the pixel 130 emitting red light, the pixel 130emitting green light, the pixel 130 emitting blue light, and the pixel130 emitting yellow light are illustrated as a pixel 130R, a pixel 130G,a pixel 130B, and a pixel 130Y, respectively. By increasing the numberof pixels 130 used as one pixel 140, the color reproducibility can beparticularly improved. Thus, the display quality of the display devicecan be improved.

Alternatively, in FIG. 7B, the coloring layers 266 corresponding to thefour pixels 130 may be red, green, blue, and white. With the pixel 130emitting white light (a pixel 130W), the luminance of the display regioncan be increased. Note that in the case of the pixel 130 emitting whitelight, it is not necessary to provide the coloring layer 266. Without awhite coloring layer 266, there is no luminance reduction at the time oftransmitting light through the coloring layer 266; thus, powerconsumption of the display device can be reduced. On the other hand,color temperature of white light can be controlled with the whitecoloring layer 266. Thus, the display quality of the display device canbe improved. Depending on the intended use of the display device, thegiven two pixels 130 of the four pixels may be used as one pixel 140.

Note that the occupation areas or shapes of the pixels 130 may be thesame or different. In addition, arrangement is not limited to stripearrangement. For example, delta arrangement, Bayer arrangement, pentilearrangement, or the like can be used. FIG. 7C illustrates an example ofthree pixels 130 arranged in a pentile pattern.

[Formation of Overcoat Layer 268]

Next, the overcoat layer 268 is formed over the light-blocking layer 264and the coloring layer 266 (see FIG. 6F).

For the overcoat layer 268, an organic insulating layer of an acrylicresin, an epoxy resin, a polyimide resin, or the like can be used. Withthe overcoat layer 268, an impurity or the like contained in thecoloring layer 266 can be inhibited from diffusing into thelight-emitting element 125 side, for example. Note that the overcoatlayer 268 is not necessarily formed.

A light-transmitting conductive film may be formed as the overcoat layer268 by which the light 151 emitted from the light-emitting element 125can pass through the overcoat layer 268 and ionized impurities can beprevented from passing through the overcoat layer 268.

The light-transmitting conductive film can be formed using, for example,indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, zincoxide to which gallium is added. Graphene or a metal film that is thinenough to have a light-transmitting property can also be used.

In this embodiment, the substrate 102 over which the coloring layer 266and the like are formed is referred to as the counter substrate 181.Through the above steps, the counter substrate 181 can be formed. Notethat the counter substrate 181 may not be provided with the coloringlayer 266 or the like.

[Attachment of Element Substrate 171 and Counter Substrate 181]

Next, the element substrate 171 and the counter substrate 181 areattached to each other with the bonding layer 120 provided therebetween.At the attachment, the light-emitting element 125 included in theelement substrate 171 and the coloring layer 266 included in the countersubstrate 181 are arranged so as to face each other (see FIG. 8A).

[Peeling of Substrate 101]

Next, the substrate 101 included in the element substrate 171 is peeledfrom the insulating layer 119 together with the peeling layer 113 (seeFIG. 8B). As a peeling method, mechanical force (a peeling process witha human hand or a gripper, a separation process by rotation of a roller,ultrasonic waves, or the like) may be used. For example, a cut is madein the interface between the peeling layer 113 and the insulating layer119 from the side surface of the element substrate 171 with a sharpedged tool, by laser beam irradiation, or the like and water is injectedinto the cut. The interface between the peeling layer 113 and theinsulating layer 119 absorbs water by capillarity action, so that thesubstrate 101 can be peeled easily from the insulating layer 119together with the peeling layer 113.

[Attachment of Substrate 111]

Next, the substrate 111 is attached to the insulating layer 119 with thebonding layer 112 provided therebetween (see FIG. 9A).

[Peeling of Substrate 102]

Next, the substrate 102 included in the counter substrate 181 is peeledfrom the insulating layer 129 together with the peeling layer 123.

FIG. 9B illustrates a state in which the substrate 102 included in thecounter substrate 181 is peeled from the insulating layer 129 togetherwith the peeling layer 123. At this time, an opening 132 a is formed byremoval of part of the bonding layer 120 overlapping substantially withthe opening 139 and the peeling layer 110 b overlapping substantiallywith the opening 139. Alternatively, the opening 132 a is formed byremoval of the bonding layer 120 overlapping substantially with theopening 139, the peeling layer 110 b overlapping substantially with theopening 139, and part of the peeling layer 110 a overlappingsubstantially with the opening 139. Note that the substrate 102 ispreferably arranged such that the opening 139 is placed on the innerside than the electrode 116, in which case the opening 132 a can beformed easily. That is, it is preferable that the opening 132 a beformed on the inner side than the end portion of the electrode 116 inthe cross-sectional view. The width W1 of the opening 139 is preferablysmaller than the width W2 of the surface where the peeling layer 110 aand the peeling layer 110 b are in contact with each other, in whichcase the peeling layer 110 b is easily peeled from the peeling layer 110a (see FIG. 9A).

Meanwhile, when the width W1 is smaller than the width W2, a part of thepeeling layer 110 b, which does not overlap with the opening 132 a,might be lifted at peeling from the peeling layer 110 a in a directiondiagonal to the perpendicular direction. Accordingly, in some cases,this part and a part of the bonding layer 120 overlapping therewith, andthe like are separated from the interface with the peeling layer 110 aand remain on the peeling layer 110 a. Therefore, it is preferable thata difference between the width W1 and the width W2 be small.

Note that after the substrate 102 is peeled from the insulating layer129, the peeling layer 110 a might remain on the electrode 116. When thepeeling layer 110 a remains on the electrode 116, contact failure mightbe caused between the electrode 116 and the anisotropic conductiveconnection layer 138. Therefore, after the substrate 102 is peeled, theremaining peeling layer 110 a which is attached to the electrode 116 ispreferably removed with, for example, an organic solvent such asacetone. In this embodiment, the peeling layer 110 a on the electrode116 is removed with acetone. Note that the peeling layer 110 a remainingon the electrode 116 is not necessarily removed in the case where itdoes not cause a problem in electrical connection between the electrode116 and the anisotropic conductive connection layer 138 in the presenceof the peeling layer 110 a.

[Attachment of Substrate 121]

Next, the substrate 121 having an opening 132 b is attached to theinsulating layer 129 with the bonding layer 122 provided therebetween(see FIG. 10A). The substrate 121 and the insulating layer 129 areattached to each other so that the opening 132 a overlaps with theopening 132 b. In this embodiment, the openings 132 a and 132 b arecollectively referred to as an opening 132. The surface of the electrode116 is exposed from the opening 132.

At the attachment of the substrate 121 to the insulating layer 129, thewidth of the opening 132 b, the amount of an adhesive used for thebonding layer 122, or the like is preferably adjusted so that thebonding layer 122 covers side surfaces of the layers in the opening 132a as illustrated in FIG. 10B. With such a structure, a break or a crackof the insulating layer 129 and the like which are exposed in the sidesurfaces of the opening 132 a can be suppressed. Moreover, after theremoval of the peeling layer 110 b, the peeling layer 110 remaining onthe insulating layer 141 in the vicinity of the opening 132 a is coveredwith the bonding layer 122, so that diffusion of the material forforming the peeling layer 110 into the anisotropic conductive connectionlayer 138 can be suppressed. For example, the width W3 of the opening132 b is preferably smaller than the width W4 of the opening 132 (seeFIG. 10B). FIG. 10B is a cross-sectional view of the display device 100after the attachment of the substrate 121 to the insulating layer 129.

In the display device 100 of one embodiment of the present invention, aplurality of electrodes 116 may be provided in one opening 132 or theopening 132 may be provided for each electrode 116. FIG. 11A is aperspective view of the display device 100 in which a plurality ofelectrodes 116 are provided in one opening 132, and FIG. 11B is across-sectional view taken along the dashed-dotted line B1-B2 in FIG.11A. FIG. 12A is a perspective view of the display device 100 in whichthe opening 132 is provided for each electrode 116, and FIG. 12B is across-sectional view taken along the dashed-dotted line B3-B4 in FIG.12A.

The opening 132 is provided on the inner side than the end portion ofthe substrate 121 in a plan view, so that the outer edge of the opening132 can be supported by the substrate 121 and the substrate 111. Thus,the mechanical strength of a region where the external electrode 124 andthe electrode 116 are connected to each other is unlikely to decrease,and unintentional deformation of the connected region can be reduced.Note that an effect of reducing the deformation of the connected regioncan be improved in the case where the opening 132 is provided for eachelectrode 116 as compared with the case where a plurality of electrodes116 are provided in one opening 132 (see FIG. 12B). According to oneembodiment of the present invention, breakage of the display device 100can be prevented, and the reliability of the display device 100 can beimproved.

Alternatively, one or more of layers each formed using a material havinga specific function, such as an anti-reflection layer, a light diffusionlayer, a microlens array, a prism sheet, a retardation plate, or apolarizing plate, (hereinafter referred to as “functional layers”) maybe provided on an outer side than the substrate 111 or the substrate 121from which the light 151 is emitted. As the anti-reflection layer, forexample, a circularly polarizing plate can be used. With the functionallayer, a display device having a higher display quality can be achieved.Moreover, power consumption of the display device can be reduced.

FIG. 13A is a cross-sectional view of the display device 100 having atop-emission structure including a functional layer 161. FIG. 13B is across-sectional view of the display device 100 having a bottom-emissionstructure including the functional layer 161. FIG. 13C is across-sectional view of the display device 100 having a dual-emissionstructure including the functional layer 161.

For the substrate 111 or the substrate 121, a material having a specificfunction may be used. For example, a circularly polarizing plate may beused as the substrate 111 or the substrate 121. Alternatively, forexample, the substrate 111 or the substrate 121 may be formed using aretardation plate, and a polarizing plate may be provided so as tooverlap with the substrate. As another example, the substrate 111 or thesubstrate 121 may be formed using a prism sheet, and a circularlypolarizing plate may be provided so as to overlap with the substrate.With the use of the material having a specific function for thesubstrate 111 or the substrate 121, improvement of display quality andreduction of the manufacturing cost can be achieved.

Note that in consideration of mass production, a plurality of displaydevices 100 are preferably manufactured from one substrate in such amanner that the plurality of display devices 100 are manufactured over alarge-sized substrate at a time and then the large-sized substrate isdivided, in which case reduction in manufacturing cost can be achieved.In the case of obtaining a plurality of display devices from onesubstrate, the individual display devices 100 can be manufactured bydividing the large-sized substrate after the attachment of the substrate121, for example. As will be described later in Embodiment 2, in thecase where a display device includes a transistor and the like, astructure in which a short ring can be divided at the same time asdivision of the substrate is preferable. The short ring is a wiring forshort-circuiting a plurality of wirings for supplying voltage to aplurality of circuits to prevent current from locally flowing into acertain circuit including a transistor in the case where overcurrent iscaused in part of the display device during the manufacturing process ofthe display device.

[Formation of External Electrode 124]

Next, the anisotropic conductive connection layer 138 is formed in andon the opening 132, and the external electrode 124 for inputtingelectric power or a signal to the display device 100 is formed over theanisotropic conductive connection layer 138 (see FIGS. 1A and 1B). Theelectrode 116 is electrically connected to the external electrode 124through the anisotropic conductive connection layer 138. Thus, electricpower or a signal can be input to the display device 100. Note that anFPC can be used as the external electrode 124. A metal wire can also beused as the external electrode 124. Although the anisotropic conductiveconnection layer 138 may be used to connect the metal wire and theelectrode 116 to each other, the connection may be performed by a wirebonding method without using the anisotropic conductive connection layer138. Alternatively, the metal wire and the electrode 116 may beconnected to each other by a soldering method.

This embodiment can be implemented in an appropriate combination withany of the structures described in the other embodiments.

Embodiment 2

In this embodiment, a display device 200 having a structure differentfrom the structure of the display device 100 described in the aboveembodiment will be described with reference to FIGS. 14A and 14B. FIG.14A is a perspective view of the display device 200, and FIG. 14B is across-sectional view taken along the dashed-dotted line A5-A6 in FIG.14A.

<Structure of Display Device>

The display device 200 described in this embodiment includes a displayregion 231 and a peripheral circuit 251. The display device 200 furtherincludes the electrode 116 and the light-emitting element 125 includingthe electrode 115, the EL layer 117, and the electrode 118. A pluralityof light-emitting elements 125 are formed in the display region 231. Atransistor 232 for controlling the amount of light emitted from thelight-emitting element 125 is connected to each light-emitting element125.

The electrode 116 is electrically connected to the external electrode124 through the anisotropic conductive connection layer 138 formed inthe opening 132. Although not illustrated, the electrode 116 iselectrically connected to the peripheral circuit 251.

The peripheral circuit 251 includes a plurality of transistors 252. Theperipheral circuit 251 has a function of determining which of thelight-emitting elements 125 in the display region 231 is supplied with asignal from the external electrode 124.

In the display device 200 illustrated in FIGS. 14A and 14B, thesubstrate 111 and the substrate 121 are attached to each other with thebonding layer 120 provided therebetween. An insulating layer 205 isformed over the substrate 111 with the bonding layer 112 providedtherebetween. The insulating layer 205 is preferably formed as a singlelayer or a multilayer using any of silicon oxide, silicon nitride,silicon oxynitride, silicon nitride oxide, aluminum oxide, aluminumoxynitride, and aluminum nitride oxide. The insulating layer 205 can beformed by a sputtering method, a CVD method, a thermal oxidation method,a coating method, a printing method, or the like.

The insulating layer 205 functions as a base layer and can prevent orreduce diffusion of impurity elements from the substrate 111, thebonding layer 112, or the like to the transistor or the light-emittingelement.

The transistor 232, the transistor 252, the electrode 116, and a wiring219 are formed over the insulating layer 205. Although a channel-etchedtransistor that is a type of bottom-gate transistor is illustrated asthe transistor 232 and/or the transistor 252 in this embodiment, achannel-protective transistor, a top-gate transistor, or the like canalso be used. Alternatively, an inverted staggered transistor or aforward staggered transistor can also be used. It is also possible touse a dual-gate transistor, in which a semiconductor layer in which achannel is formed is provided between two gate electrodes. Furthermore,the transistor is not limited to a transistor having a single-gatestructure; a multi-gate transistor having a plurality of channelformation regions, such as a double-gate transistor, may be used.

As the transistor 232 and the transistor 252, a transistor with any of avariety of structures such as a planar type, a FIN-type, and a Tri-Gatetype can be used.

The transistor 232 and the transistor 252 may have the same structure ordifferent structures. The size (e.g., channel length and channel width)or the like of each transistor can be adjusted as appropriate.

The transistor 232 and the transistor 252 each include an electrode 206that can function as a gate electrode, an insulating layer 207 that canfunction as a gate insulating layer, a semiconductor layer 208, anelectrode 214 that can function as one of a source electrode and a drainelectrode, and an electrode 215 that can function as the other of thesource electrode and the drain electrode.

The wiring 219, the electrode 214, and the electrode 215 can be formedat the same time as the electrode 116 using part of the conductivelayers for forming the electrode 116. The insulating layer 207 can beformed using a material and a method similar to those of the insulatinglayer 205.

The semiconductor layer 208 can be formed using a single crystalsemiconductor, a polycrystalline semiconductor, a microcrystallinesemiconductor, a nanocrystal semiconductor, a semi-amorphoussemiconductor, an amorphous semiconductor, or the like. For example,amorphous silicon or microcrystalline germanium can be used.Alternatively, a compound semiconductor such as silicon carbide, galliumarsenide, an oxide semiconductor, or a nitride semiconductor, an organicsemiconductor, or the like can be used. In the case of using an oxidesemiconductor for the semiconductor layer 208, a c-axis alignedcrystalline oxide semiconductor (CAAC-OS), a polycrystalline oxidesemiconductor, a microcrystalline oxide semiconductor, a nanocrystallineoxide semiconductor (nc-OS), an amorphous oxide semiconductor, or thelike can be used.

Note that an oxide semiconductor has an energy gap as wide as 3.0 eV ormore and high visible-light transmissivity. In a transistor obtained byprocessing an oxide semiconductor under appropriate conditions, it ispossible to realize an extremely low off-state current (current flowingbetween a source and drain in an off state of a transistor). Forexample, the off-state current per 1 μm of a channel width can be lessthan or equal to 100 zA (1×10⁻¹⁹ A), less than or equal to 10 zA(1×10⁻²⁰ A), and further less than or equal to 1 zA (1×10⁻²¹ A) when thesource-drain voltage is 3.5 V at 25° C. Therefore, a display device withlow power consumption can be achieved.

In the case where an oxide semiconductor is used for the semiconductorlayer 208, an insulating layer containing oxygen is preferably used asan insulating layer in contact with the semiconductor layer 208. For theinsulating layer in contact with the semiconductor layer 208, it isparticularly preferable to use an insulating layer from which oxygen isreleased by heat treatment.

An insulating layer 210 is formed over the transistor 232 and thetransistor 252, and an insulating layer 211 is formed over theinsulating layer 210. The insulating layers 210 and 211 each function asa protective insulating layer and can prevent or reduce diffusion ofimpurity elements from a layer above the insulating layer 211 to thetransistor 232 and the transistor 252. The insulating layers 210 and 211each can be formed using a material and a method similar to those of theinsulating layer 205.

An interlayer insulating layer 212 is formed over the insulating layer211. The interlayer insulating layer 212 can absorb the unevennesscaused by the transistor 232 and the transistor 252. Planarizationtreatment may be performed on a surface of the interlayer insulatinglayer 212. The planarization treatment may be, but not particularlylimited to, polishing treatment (e.g., chemical mechanical polishing(CMP)) or dry etching treatment.

Forming the interlayer insulating layer 212 using an insulating materialhaving a planarization function can omit polishing treatment. As theinsulating material having a planarization function, for example, anorganic material such as a polyimide resin or an acrylic resin can beused. Other than the above-described organic materials, it is alsopossible to use a low-dielectric constant material (low-k material) orthe like. Note that the interlayer insulating layer 212 may be formed bystacking a plurality of insulating films formed of these materials.

Over the interlayer insulating layer 212, the light-emitting element 125and the partition 114 for separating the adjacent light-emittingelements 125 are formed. The electrode 115 is also formed in the opening132 so as to overlap with the electrode 116.

The substrate 121 is provided with the light-blocking layer 264, thecoloring layer 266, and the overcoat layer 268. The display device 200is what is called a top-emission light-emitting device, in which lightemitted from the light-emitting element 125 is extracted from thesubstrate 121 side through the coloring layer 266.

The light-emitting element 125 is electrically connected to thetransistor 232 through an opening formed in the interlayer insulatinglayer 212 and insulating layers 211 and 210.

With a micro optical resonator (also referred to as microcavity)structure which allows light emitted from the EL layer 117 to resonate,lights with different wavelengths and narrowed spectra even when one ELlayer 117 is used for different light-emitting elements 125.

FIGS. 15A and 15B are cross-sectional views of the display device 200 inwhich the light-emitting element 125 has a microcavity structure, forexample. Note that FIG. 15A corresponds to a cross-sectional view takenalong the vicinity of the dashed-dotted line A5-A6 in FIG. 14A. FIG. 15Bis an enlarged view of a portion 280 in FIG. 15A.

In the case where the light-emitting element 125 has a microcavitystructure, the electrode 118 is formed using a conductive material (asemi-transmissive material) which transmits and reflect a certain amountof light of the incident light, and the electrode 115 is formed using astack of a conductive material having high reflectance (the reflectanceof visible light is 50% or more and 100% or less, or preferably 70% ormore and 100% or less) and a conductive material having hightransmittance (the transmittance of visible light is 50% or more and100% or less, or preferably 70% or more and 100% or less). Here, theelectrode 115 is formed of a stack of an electrode 115 a formed using aconductive material that reflects light and an electrode 115 b formedusing a conductive material that transmits light. The electrode 115 b isprovided between the EL layer 117 and the electrode 115 a (see FIG.15B). The electrode 115 a functions as a reflective electrode, and theelectrode 118 functions as a semi-reflective electrode.

For example, the electrode 118 may be formed using a conductive materialcontaining silver (Ag) or a conductive material containing aluminum (Al)having a thickness of 1 nm to 30 nm, or preferably 1 nm to 15 nm. Inthis embodiment, as the electrode 118, a 10-nm-thick conductive materialcontaining silver and magnesium is used.

The electrode 115 a may be formed using a conductive material containingsilver (Ag) or a conductive material containing aluminum (Al) having athickness of 50 nm to 500 nm, or preferably 50 nm to 200 nm. In thisembodiment, the electrode 115 a is formed using a 100-nm-thickconductive material containing silver.

For the electrode 115 b, a conductive oxide containing indium (In) or aconductive oxide containing zinc (Zn) having a thickness of 1 nm to 200nm or preferably 5 nm to 100 nm may be used. In this embodiment, indiumtin oxide is used for the electrode 115 b. Furthermore, a conductiveoxide may be provided under the electrode 115 a.

By changing the thickness t of the electrode 115 b, a distance d fromthe interface between the electrode 118 and the EL layer 117 to theinterface between the electrode 115 a and the electrode 115 b can be setto an arbitral value. The light-emitting elements 125 having differentemission spectra for respective pixels can be provided even when one ELlayer 117 is used by changing the thickness t of the electrode 115 b ineach pixel. Thus, color purity of each emission color is improved and adisplay device having favorable color reproducibility can be achieved.It is not necessary to independently form the EL layer 117 in each pixeldepending on the emission color; therefore, the number of manufacturingsteps of the display device can be reduced and thus the productivity canbe improved. Furthermore, a high-definition display device can beachieved easily.

Note that a method for adjusting the distance d is not limited to theabove method. For example, the distance d may be adjusted by changingthe film thickness of the EL layer 117.

FIG. 15A shows an example in which the pixel 130R, the pixel 130G, thepixel 130B, and the pixel 130Y that emit red light 151R, green light151G, blue light 151B, and yellow light 151Y, respectively, are used asone pixel 140. Note that one embodiment of the present invention is notlimited to this example. As the pixel 140, subpixels that emit lights ofred, green, blue, yellow, cyan, magenta, and white may be combined asappropriate. For example, the pixel 140 may be formed of the followingthree subpixels: the pixel 130R, the pixel 130G, and the pixel 130B.

The coloring layer 266 may be provided in a position overlapping withthe light-emitting element 125 so that the light 151 is emitted outsidethrough the coloring layer 266. FIG. 16 shows a structure example in thecase where the coloring layer 266 is combined with the display device200 illustrated in FIGS. 15A and 15B. In the display device 200illustrated in FIG. 16, a coloring layer 266R, a coloring layer 266G, acoloring layer 266B, and a coloring layer 266Y that transmit light in ared wavelength band, light in a green wavelength band, light in a bluewavelength band, and light in a yellow wavelength band, respectively,are provided so as to overlap with the pixel 130R that emits the redlight 151R, the pixel 130G that can emit the green light 151G, the pixel130B that can emit the blue light 151B, and the pixel 130Y that can emitthe yellow light 151Y, respectively.

By using the pixel 130Y in addition to the pixel 130R, the pixel 130G,and the pixel 130B, the color reproducibility of the display device canbe increased. In the case where the pixel 140 is formed of only thepixel 130R, the pixel 130G, and the pixel 130B, all of the pixels 130R,130G, and 130B need to emit light when white light is emitted from thepixel 140. When the pixel 130Y is provided in addition to the pixel130R, the pixel 130G, and the pixel 130B, white light can be obtained byemitting light only from the pixel 130B and the pixel 130Y. Thus, sincewhite light can be obtained even without light emission from the pixel130R and the pixel 130G, power consumption of the display device can bereduced.

Moreover, the pixel 130W that can emit white light 151W may be usedinstead of the pixel 130Y. The use of the pixel 130W instead of thepixel 130Y allows emission of white light by emitting light only fromthe pixel 130W; therefore, power consumption of the display device canbe further reduced.

Note that in the case of using the pixel 130W, a coloring layer is notnecessarily provided in the pixel 130W. Without a coloring layer, theluminance of the display region is improved and a display device havingfavorable visibility can be achieved. Moreover, power consumption of thedisplay device can be further reduced.

The pixel 130W may be provided with a coloring layer 266W that transmitslight of substantially whole of the visible region, by which the colortemperature of the white light 151W can be changed. Accordingly, adisplay device having a high display quality can be achieved.

The color purity of the light 151 can be further improved by using thelight-emitting element 125 having a microcavity structure and thecoloring layer 266 in combination. Therefore, the color reproducibilityof the display device 200 can be improved. In addition, light thatenters from the outside is mostly absorbed by the coloring layer 266;therefore, reflection of the light that enters from the outside on thedisplay region 231 is suppressed and thus the visibility of the displaydevice can be improved. Accordingly, a display device having a highdisplay quality can be achieved.

Although an active matrix display device is described as an example ofthe display device in this embodiment, one embodiment of the presentinvention can also be applied to a passive matrix display device.Moreover, one embodiment of the present invention can also be applied toa display device having a bottom-emission structure or a dual-emissionstructure.

This embodiment can be implemented in an appropriate combination withany of the structures described in the other embodiments.

Embodiment 3

In this embodiment, a specific structure example of the display device200 will be described with reference to FIGS. 17A to 17C. FIG. 17A is ablock diagram illustrating the structure example of the display device200.

The display device 200 illustrated in FIG. 17A includes the displayregion 231, a driver circuit 142 a, a driver circuit 142 b, and a drivercircuit 133. The driver circuits 142 a, 142 b, and 133 collectivelycorrespond to the peripheral circuit 251 described in the aboveembodiments. The driver circuits 142 a, 142 b, and 133 are collectivelyreferred to as a driver circuit portion in some cases.

The driver circuits 142 a and 142 b function as, for example, scan linedriver circuits. The driver circuit 133 functions as, for example, asignal line driver circuit. Note that one of the driver circuits 142 aand 142 b may be omitted. Alternatively, some sort of circuit facing thedriver circuit 133 with the display region 231 provided therebetween maybe provided.

The display device 200 includes m wirings 135 that are arrangedsubstantially parallel to each other and whose potentials are controlledby the driver circuit 142 a and/or the driver circuit 142 b, and nwirings 136 that are arranged substantially parallel to each other andwhose potentials are controlled by the driver circuit 133. The displayregion 231 includes a plurality of pixel circuits 134 arranged inmatrix. One pixel circuit 134 is used for driving one subpixel (thepixel 130).

Each of the wirings 135 is electrically connected to the n pixelcircuits 134 in a given row among the pixel circuits 134 arranged in mrows and n columns in the display region 231. Each of the wirings 136 iselectrically connected to the m pixel circuits 134 in a given columnamong the pixel circuits 134 arranged in m rows and n columns. Note thatm and n are each an integer of 1 or more.

[Example of Pixel Circuit for Display Device]

FIGS. 17B and 17C show examples of a circuit structure that can be usedfor the pixel circuits 134 in the display device in FIG. 17A.

The pixel circuit 134 illustrated in FIG. 17B includes a transistor 431,a capacitor 233, the transistor 232, and a transistor 434. The pixelcircuit 134 is electrically connected to the light-emitting element 125.

One of a source electrode and a drain electrode of the transistor 431 iselectrically connected to a wiring to which a data signal is supplied(hereinafter referred to as a signal line DL_n). A gate electrode of thetransistor 431 is electrically connected to a wiring to which a gatesignal is supplied (hereinafter referred to as a scan line GL_m). Thesignal line DL_n and the scan line GL_m correspond to the wiring 136 andthe wiring 135, respectively.

The transistor 431 has a function of controlling whether to write a datasignal to a node 435.

One of a pair of electrodes of the capacitor 233 is electricallyconnected to the node 435, and the other of the pair of electrodes ofthe capacitor 233 is electrically connected to a node 437. The other ofthe source electrode and the drain electrode of the transistor 431 iselectrically connected to the node 435.

The capacitor 233 functions as a storage capacitor for storing datawritten to the node 435.

One of a source electrode and a drain electrode of the transistor 232 iselectrically connected to a potential supply line VL_a, and the other ofthe source electrode and the drain electrode of the transistor 232 iselectrically connected to the node 437. A gate electrode of thetransistor 232 is electrically connected to the node 435.

One of a source electrode and a drain electrode of the transistor 434 iselectrically connected to a potential supply line VO, and the other ofthe source electrode and the drain electrode of the transistor 434 iselectrically connected to the node 437. A gate electrode of thetransistor 434 is electrically connected to the scan line GL_m.

One of an anode and a cathode of the light-emitting element 125 iselectrically connected to a potential supply line VL_b, and the other ofthe anode and the cathode of the light-emitting element 125 iselectrically connected to the node 437.

As the light-emitting element 125, an organic electroluminescent element(also referred to as an organic EL element) can be used, for example.Note that the light-emitting element 125 is not limited thereto and maybe an inorganic EL element containing, for example, an inorganicmaterial.

As a power supply potential, a potential on the comparatively highpotential side or a potential on the comparatively low potential sidecan be used, for example. A power supply potential on the high potentialside is referred to as a high power supply potential (also referred toas VDD), and a power supply potential on the low potential side isreferred to as a low power supply potential (also referred to as VSS). Aground potential can be used as the high power supply potential or thelow power supply potential. For example, in the case where a groundpotential is used as the high power supply potential, the low powersupply potential is a potential lower than the ground potential, and inthe case where a ground potential is used as the low power supplypotential, the high power supply potential is a potential higher thanthe ground potential.

A high power supply potential VDD is supplied to one of the potentialsupply line VL_a and the potential supply line VL_b, and a low powersupply potential VSS is supplied to the other, for example.

In the display device including the pixel circuit 134 in FIG. 17B, thepixel circuits 134 are sequentially selected row by row by the drivercircuit 142 a and/or the driver circuit 142 b, so that the transistors431 and 434 are turned on and a data signal is written to the nodes 435.

When the transistors 431 and 434 are turned off, the pixel circuits 134in which the data has been written to the nodes 435 are brought into aholding state. The amount of current flowing between the sourceelectrode and the drain electrode of the transistor 232 is controlled inaccordance with the potential of the data written to the node 435. Thelight-emitting element 125 emits light with luminance corresponding tothe amount of the flowing current. This operation is sequentiallyperformed row by row; thus, an image can be displayed.

[Example of Pixel Circuit for Liquid Crystal Display Device]

The pixel circuit 134 in FIG. 17C includes the transistor 431 and thecapacitor 233. The pixel circuit 134 is electrically connected to aliquid crystal element 432.

The potential of one of a pair of electrodes of the liquid crystalelement 432 is set in accordance with the specifications of the pixelcircuit 134 as appropriate. The alignment state of the liquid crystalelement 432 depends on data written to a node 436. A common potentialmay be applied to one of the pair of electrodes of the liquid crystalelement 432 included in each of the plurality of pixel circuits 134. Thepotential supplied to one of a pair of electrodes of the liquid crystalelement 432 in the pixel circuit 134 in one row may be different fromthe potential supplied to one of a pair of electrodes of the liquidcrystal element 432 in the pixel circuit 134 in another row.

Examples of a method for driving the display device including the liquidcrystal element 432 include a TN mode, an STN mode, a VA mode, anaxially symmetric aligned micro-cell (ASM) mode, an opticallycompensated birefringence (OCB) mode, a ferroelectric liquid crystal(FLC) mode, an antiferroelectric liquid crystal (AFLC) mode, an MVAmode, a patterned vertical alignment (PVA) mode, an IPS mode, an FFSmode, and a transverse bend alignment (TBA) mode. Other examples of themethod for driving the display device include an electrically controlledbirefringence (ECB) mode, a polymer-dispersed liquid crystal (PDLC)mode, a polymer network liquid crystal (PNLC) mode, and a guest-hostmode. Note that one embodiment of the present invention is not limitedthereto, and various liquid crystal elements and driving methods can beused.

The liquid crystal element 432 may be formed using a liquid crystalcomposition including liquid crystal exhibiting a blue phase and achiral material. The liquid crystal exhibiting a blue phase has a shortresponse time of 1 ms or less and has optical isotropy; thus, analignment process is not necessary. A liquid crystal display deviceincluding a liquid crystal exhibiting a blue phase has small viewingangle dependence because the liquid crystal has optical isotropy.

In the pixel circuit 134 in the m-th row and the n-th column, one of thesource electrode and the drain electrode of the transistor 431 iselectrically connected to the signal line DL_n, and the other of thesource electrode and the drain electrode of the transistor 431 iselectrically connected to the node 436. The gate electrode of thetransistor 431 is electrically connected to the scan line GL_m. Thetransistor 431 has a function of controlling whether to write a datasignal to the node 436.

One of the pair of electrodes of the capacitor 233 is electricallyconnected to a wiring to which a specific potential is supplied(hereinafter referred to as a capacitor line CL), and the other of thepair of electrodes of the capacitor 233 is electrically connected to thenode 436. The other of the pair of electrodes of the liquid crystalelement 432 is electrically connected to the node 436. The potential ofthe capacitor line CL is set in accordance with the specifications ofthe pixel circuit 134 as appropriate. The capacitor 233 functions as astorage capacitor for storing data written to the node 436.

For example, in the display device including the pixel circuit 134 inFIG. 17C, the pixel circuits 134 are sequentially selected row by row bythe driver circuit 142 a and/or the driver circuit 142 b, so that thetransistors 431 are turned on and a data signal is written to the nodes436.

When the transistors 431 are turned off, the pixel circuits 134 in whichthe data signal has been written to the nodes 436 are brought into aholding state. This operation is sequentially performed row by row;thus, an image can be displayed on the display region 231.

[Display Element]

The display device of one embodiment of the present invention can employvarious modes and can include various elements. The display elementincludes at least one of an electroluminescence (EL) element (e.g., anEL element including organic and inorganic materials, an organic ELelement, or an inorganic EL element) including, an LED (e.g., a whiteLED, a red LED, a green LED, or a blue LED), a transistor (a transistorthat emits light depending on current), an electron emitting element, aplasma display panel (PDP), a liquid crystal element, an electrophoreticelement, a display element using micro electro mechanical system (MEMS)such as a grating light valve (GLV), a digital micromirror device (DMD),a digital micro shutter (DMS) element, a MIRASOL (registered trademark)display, an interferometric modulator display (IMOD) element, and apiezoelectric ceramic display, an electrowetting element, and the like.Other than the above, the display device may contain a display mediumwhose contrast, luminance, reflectance, transmittance, or the like ischanged by electrical or magnetic action. Alternatively, quantum dotsmay be used as the display element. Examples of display devices havingEL elements include an EL display. Examples of a display deviceincluding an electron emitter include a field emission display (FED) andan SED-type flat panel display (SED: surface-conduction electron-emitterdisplay). Examples of display devices including quantum dots include aquantum dot display. Examples of display devices including liquidcrystal elements include a liquid crystal display (e.g., a transmissiveliquid crystal display, a transflective liquid crystal display, areflective liquid crystal display, a direct-view liquid crystal display,or a projection liquid crystal display). Examples of display deviceshaving electrophoretic elements include electronic paper. In the case ofa transflective liquid crystal display or a reflective liquid crystaldisplay, some or all of pixel electrodes function as reflectiveelectrodes. For example, some or all of pixel electrodes are formed tocontain aluminum, silver, or the like. In such a case, a memory circuitsuch as an SRAM can be provided under the reflective electrodes, leadingto lower power consumption.

This embodiment can be implemented in an appropriate combination withany of the structures described in the other embodiments.

Embodiment 4

In this embodiment, an example of a transistor which can be used insteadof the transistor 232 and/or the transistor 252 described in the aboveembodiments will be described with reference to FIGS. 18A1, 18A2, 18B1,and 18B2. A transistor disclosed in this specification and the like canbe applied to the transistors 431, 434, and the like.

[Bottom-Gate Transistor]

A transistor 410 shown in FIG. 18A1 as an example is achannel-protective transistor that is a type of bottom-gate transistor.The transistor 410 includes an insulating layer 209 that can function asa channel protective layer over a channel formation region in thesemiconductor layer 208. The insulating layer 209 can be formed using amaterial and a method that are similar to those of the insulating layer205 described in Embodiment 2. Part of the electrode 214 and part of theelectrode 215 are formed over the insulating layer 209.

With the insulating layer 209 provided over the channel formationregion, the semiconductor layer 208 can be prevented from being exposedat the time of forming the electrode 214 and the electrode 215. Thus,the semiconductor layer 208 can be prevented from being reduced inthickness at the time of forming the electrode 214 and the electrode215.

A transistor 411 illustrated in FIG. 18A2 is different from thetransistor 410 in that an electrode 213 that can function as a back gateelectrode is provided over the insulating layer 211. The electrode 213can be formed using a material and a method that are similar to those ofthe electrode 206. The electrode 213 may be formed between theinsulating layer 210 and the insulating layer 211.

In general, the back gate electrode is formed using a conductive layerand positioned so that the channel formation region of the semiconductorlayer is provided between the gate electrode and the back gateelectrode. Thus, the back gate electrode can function in a mannersimilar to that of the gate electrode. The potential of the back gateelectrode may be the same as that of the gate electrode or may be a GNDpotential or a predetermined potential. By changing a potential of theback gate electrode independently of the potential of the gateelectrode, the threshold voltage of the transistor can be changed.

The electrodes 206 and 213 can both function as a gate electrode. Thus,the insulating layers 207, 209, 210, and 211 can all function as a gateinsulating layer.

In the case where one of the electrode 206 and the electrode 213 issimply referred to as a “gate electrode”, the other can be referred toas a “back gate electrode”. For example, in the transistor 411, in thecase where the electrode 213 is referred to as a “gate electrode”, theelectrode 206 is referred to as a “back gate electrode”. In the casewhere the electrode 213 is used as a “gate electrode”, the transistor411 is a kind of bottom-gate transistor. Furthermore, one of theelectrode 206 and the electrode 213 might be referred to as a “firstgate electrode”, and the other might be referred to as a “second gateelectrode”.

By providing the electrode 206 and the electrode 213 with thesemiconductor layer 208 provided therebetween and setting the potentialsof the electrode 206 and the electrode 213 to be the same, a region ofthe semiconductor layer 208 through which carriers flow is enlarged inthe film thickness direction; thus, the number of transferred carriersis increased. As a result, the on-state current and the field-effectmobility of the transistor 411 are increased.

Therefore, the transistor 411 has large on-state current for the areaoccupied thereby. That is, the area occupied by the transistor 411 canbe small for required on-state current.

Furthermore, the gate electrode and the back gate electrode are formedusing conductive layers and thus each have a function of preventing anelectric field generated outside the transistor from influencing thesemiconductor layer in which the channel is formed (in particular, afunction of blocking static electricity).

Since the electrode 206 and the electrode 213 each have a function ofblocking an electric field generated outside, charges of chargedparticles and the like generated on the substrate 111 side or above theelectrode 213 do not influence the channel formation region in thesemiconductor layer 208. Therefore, degradation in a BT stress test(e.g., a negative gate bias temperature (−GBT) stress test in whichnegative charges are applied to a gate) can be reduced, and changes inthe threshold voltage can be reduced. Note that this effect is causedwhen the electrodes 206 and 213 have the same potential or differentpotentials.

The BT stress test is one kind of accelerated test and can evaluate, ina short time, a change by long-term use (i.e., a change over time) incharacteristics of transistors. In particular, the change in thresholdvoltage of the transistor between before and after the BT stress test isan important indicator when examining the reliability of the transistor.If the change in the threshold voltage between before and after the BTstress test is smaller, the transistor has higher reliability.

By providing the electrode 206 and the electrode 213 and setting thepotentials of the electrode 206 and the electrode 213 to be the same,the change in threshold voltage is reduced. Accordingly, variation inelectrical characteristics among a plurality of transistors is alsoreduced.

The transistor including the back gate electrode has a smaller change inthreshold voltage between before and after a positive GBT stress test inwhich positive charges are applied to a gate than a transistor includingno back gate electrode.

When the back gate electrode is formed using a light-blocking conductivefilm, light can be prevented from entering the semiconductor layer fromthe back gate electrode side. Therefore, photodegradation of thesemiconductor layer can be prevented and deterioration in electricalcharacteristics of the transistor, such as a shift of the thresholdvoltage, can be prevented.

A transistor 420 shown in FIG. 18B1 as an example is achannel-protective transistor that is a type of bottom-gate transistor.The transistor 420 has substantially the same structure as thetransistor 410 but is different from the transistor 410 in that theinsulating layer 209 covers the side surfaces of the semiconductor layer208.

The semiconductor layer 208 is electrically connected to the electrode214 in an opening which is formed by selectively removing part of theinsulating layer 209. The semiconductor layer 208 is electricallyconnected to the electrode 215 in the opening which is formed byselectively removing part of the insulating layer 209. A region of theinsulating layer 209 which overlaps with the channel formation regioncan function as a channel protective layer.

A transistor 421 illustrated in FIG. 18B2 is different from thetransistor 420 in that the electrode 213 that can function as a backgate electrode is provided over the insulating layer 211.

With the insulating layer 209, the semiconductor layer 208 can beprevented from being exposed at the time of forming the electrode 214and the electrode 215. Thus, the semiconductor layer 208 can beprevented from being reduced in thickness at the time of forming theelectrode 214 and the electrode 215.

The length between the electrode 214 and the electrode 206 and thelength between the electrode 215 and the electrode 206 in thetransistors 420 and 421 are longer than those in the transistors 410 and411. Thus, the parasitic capacitance generated between the electrode 214and the electrode 206 can be reduced. Moreover, the parasiticcapacitance generated between the electrode 215 and the electrode 206can be reduced.

[Top-Gate Transistor]

A transistor 430 shown in FIG. 19A1 as an example is a type of top-gatetransistor. The transistor 430 includes the semiconductor layer 208 overthe insulating layer 119; the electrode 214 in contact with part of thesemiconductor layer 208 and the electrode 215 in contact with part ofthe semiconductor layer 208, over the semiconductor layer 208 and theinsulating layer 119; the insulating layer 207 over the semiconductorlayer 208, the electrode 214 and the electrode 215; and the electrode206 over the insulating layer 207. The insulating layer 210 and theinsulating layer 211 are formed over the electrode 206.

Since, in the transistor 430, the electrode 206 overlaps with neitherthe electrode 214 nor the electrode 215, the parasitic capacitancegenerated between the electrode 206 and the electrode 214 and theparasitic capacitance generated between the electrode 206 and theelectrode 215 can be reduced. After the formation of the electrode 206,an impurity element 221 is introduced into the semiconductor layer 208using the electrode 206 as a mask, so that an impurity region can beformed in the semiconductor layer 208 in a self-aligned manner (see FIG.19A3).

The introduction of the impurity element 221 can be performed with anion implantation apparatus, an ion doping apparatus, or a plasmatreatment apparatus.

As the impurity element 221, for example, at least one element of aGroup 13 element and a Group 15 element can be used. In the case wherean oxide semiconductor is used for the semiconductor layer 208, it ispossible to use at least one kind of element of a rare gas, hydrogen,and nitrogen as the impurity element 221.

A transistor 431 illustrated in FIG. 19A2 is different from thetransistor 430 in that the electrode 213 and an insulating layer 217 areincluded. The transistor 431 includes the electrode 213 formed over theinsulating layer 119 and the insulating layer 217 formed over theelectrode 213. As described above, the electrode 213 can function as aback gate electrode. Thus, the insulating layer 217 can function as agate insulating layer. The insulating layer 217 can be formed using amaterial and a method that are similar to those of the insulating layer205.

The transistor 431 as well as the transistor 411 has large on-statecurrent for the area occupied thereby. That is, the area occupied by thetransistor 431 can be small for required on-state current. According toone embodiment of the present invention, the area occupied by atransistor can be reduced. Therefore, according to one embodiment of thepresent invention, a semiconductor device having a high degree ofintegration can be provided.

Transistor 440 and 441 exemplified in FIGS. 19B1 and 19B2 are each atype of top-gate transistor. The transistors 440 and 441 are differentfrom the transistors 430 and 431, respectively, in that thesemiconductor layers 208 are formed after the formation of theelectrodes 214 and the electrodes 215. Thus, in the transistors 440 and441, part of the semiconductor layer 208 is formed over the electrode214 and another part of the semiconductor layer 208 is formed over theelectrode 215.

The transistor 441 as well as the transistor 411 has large on-statecurrent for the area occupied thereby. That is, the area occupied by thetransistor 441 can be small for required on-state current. Therefore, asemiconductor device having a high degree of integration can beprovided.

In the transistors 440 and 441, after the formation of the electrode206, the impurity element 221 is introduced into the semiconductor layer208 using the electrode 206 as a mask, so that an impurity region can beformed in the semiconductor layer 208 in a self-aligned manner.

Although the variety of films such as the metal film, the semiconductorfilm, the inorganic insulating film which are disclosed in thisspecification and the like can be formed by a sputtering method or aplasma chemical vapor deposition (CVD) method, such films may be formedby another method, for example, a thermal CVD method. A metal organicchemical vapor deposition (MOCVD) method or an atomic layer deposition(ALD) method may be employed as an example of a thermal CVD method.

A thermal CVD method has an advantage that no defect due to plasmadamage is generated because it does not utilize plasma for forming afilm.

Deposition by a thermal CVD method may be performed in such a mannerthat a source gas and an oxidizer are supplied to a chamber at a time,the pressure in the chamber is set to an atmospheric pressure or areduced pressure, and they are reacted with each other in the vicinityof the substrate or over the substrate.

Deposition by an ALD method may be performed in such a manner that thepressure in a chamber is set to an atmospheric pressure or a reducedpressure, source gases for reaction are sequentially introduced into thechamber, and then the sequence of the gas introduction is repeated. Forexample, two or more kinds of source gases are sequentially supplied tothe chamber by switching respective switching valves (also referred toas high-speed valves). For example, a first source gas is introduced, aninert gas (e.g., argon or nitrogen) or the like is introduced at thesame time as or after the introduction of the first source gas so thatthe source gases are not mixed, and then a second source gas isintroduced. Note that in the case where the first source gas and theinert gas are introduced at a time, the inert gas serves as a carriergas, and the inert gas may also be introduced at the same time as theintroduction of the second source gas. Alternatively, the first sourcegas may be exhausted by vacuum evacuation instead of the introduction ofthe inert gas, and then the second source gas may be introduced. Thefirst source gas is adsorbed on a surface of the substrate to form afirst thin layer; then the second source gas is introduced to react withthe first thin layer; as a result, a second thin layer is stacked overthe first thin layer, so that a thin film is formed. The sequence of thegas introduction is controlled and repeated plural times until a desiredthickness is obtained, whereby a thin film with excellent step coveragecan be formed. The thickness of the thin film can be adjusted by thenumber of repetition times of the sequence of the gas introduction;therefore, an ALD method makes it possible to accurately adjust the filmthickness and thus is suitable for manufacturing a minute FET.

The variety of films such as the metal film, the semiconductor film, andthe inorganic insulating film which are described in the aboveembodiments can be formed by a thermal CVD method such as a MOCVD methodor an ALD method. For example, in the case where an In—Ga—Zn—O film isformed, trimethylindium (In(CH₃)₃), trimethylgallium (Ga(CH₃)₃), anddimethylzinc (Zn(CH₃)₂) are used. Without limitation to the abovecombination, triethylgallium (Ga(C₂H₅)₃) can be used instead oftrimethylgallium, and diethylzinc (Zn(C₂H₅)₂) can be used instead ofdimethylzinc.

For example, in the case where a hafnium oxide film is formed by adeposition apparatus using an ALD method, two kinds of gases, i.e.,ozone (O₃) as an oxidizer and a source gas which is obtained byvaporizing liquid containing a solvent and a hafnium precursor compound(a hafnium alkoxide or hafnium amide such as tetrakis(dimethylamide)hafnium (TDMAH, Hf[N(CH₃)₂]₄)) are used. Examples ofanother material liquid include tetrakis(ethylmethylamide)hafnium.

For example, in the case where an aluminum oxide film is formed by adeposition apparatus using an ALD method, two kinds of gases, e.g., H₂Oas an oxidizer and a source gas which is obtained by vaporizing asolvent and liquid containing an aluminum precursor compound (e.g.,trimethylaluminum (TMA, Al(CH₃)₃)) are used. Examples of anothermaterial liquid include tris (dimethylamide)aluminum,triisobutylaluminum, and aluminum tris(2,2,6,6-tetramethyl-3,5-heptanedionate).

For example, in the case where a silicon oxide film is formed by adeposition apparatus using an ALD method, hexachlorodisilane is adsorbedon a surface where a film is to be formed, and radicals of an oxidizinggas (e.g., O₂ or dinitrogen monoxide) are supplied to react with theadsorbate.

For example, in the case where a tungsten film is formed by a depositionapparatus using an ALD method, a WF₆ gas and a B₂H₆ gas are sequentiallyintroduced plural times to form an initial tungsten film, and then a WF₆gas and an H₂ gas are sequentially introduced plural times to form atungsten film. Note that an SiH₄ gas may be used instead of a B₂H₆ gas.

For example, in the case where an oxide semiconductor film, for example,an In—Ga—Zn—O film is formed by a deposition apparatus using an ALDmethod, an In(CH₃)₃ gas and an O₃ gas are sequentially introduced pluraltimes to form an In—O layer, a Ga(CH₃)₃ gas and an O₃ gas aresequentially introduced plural times to form a GaO layer, and then aZn(CH₃)₂ gas and an O₃ gas are sequentially introduced plural times toform a ZnO layer. Note that the order of these layers is not limited tothis example. A mixed oxide layer such as an In—Ga—O layer, an In—Zn—Olayer, or a Ga—Zn—O layer may be formed by using these gases. Note thatalthough an H₂O gas which is obtained by bubbling water with an inertgas such as Ar may be used instead of an O₃ gas, it is preferable to usean O₃ gas, which does not contain H. Furthermore, instead of an In(CH₃)₃gas, an In(C₂H₅)₃ gas may be used. Instead of a Ga(CH₃)₃ gas, aGa(C₂H₅)₃ gas may be used. Alternatively, a Zn(CH₃)₂ gas may be used.

This embodiment can be implemented in an appropriate combination withany of the structures described in the other embodiments.

Embodiment 5

In this embodiment, structure examples of a light-emitting element thatcan be used as the light-emitting element 125 will be described. Notethat an EL layer 320 described in this embodiment corresponds to the ELlayer 117 described in the other embodiments.

<Structure of Light-Emitting Element>

In a light-emitting element 330 illustrated in FIG. 20A, the EL layer320 is sandwiched between a pair of electrodes (electrodes 318 and 322).The electrode 318, the electrode 322, and the EL layer 320 respectivelycorrespond to the electrode 115, the electrode 118, and the EL layer 117of the aforementioned Embodiments. Note that the electrode 318 is usedas an anode and the electrode 322 is used as a cathode as an example inthe following description of this embodiment.

The EL layer 320 includes at least a light-emitting layer and may have astacked-layer structure including a functional layer other than thelight-emitting layer. As the functional layer other than thelight-emitting layer, a layer containing a substance having a highhole-injection property, a substance having a high hole-transportproperty, a substance having a high electron-transport property, asubstance having a high electron-injection property, a bipolar substance(a substance having high electron and hole transport properties), or thelike can be used. Specifically, functional layers such as ahole-injection layer, a hole-transport layer, an electron-transportlayer, and an electron-injection layer can be used in appropriatecombination.

The light-emitting element 330 illustrated in FIG. 20A emits light whencurrent flows by applying a potential difference between the electrode318 and the electrode 322 and holes and electrons are recombined in theEL layer 320. In other words, a light-emitting region is formed in theEL layer 320.

In one embodiment of the present invention, light emitted from thelight-emitting element 330 is extracted to the outside from theelectrode 318 side or the electrode 322 side. Thus, one of theelectrodes 318 and 322 is formed using a light-transmitting substance.

Note that a plurality of EL layers 320 may be stacked between theelectrode 318 and the electrode 322 as in a light-emitting element 331illustrated in FIG. 20B. In the case where n (n is a natural number of 2or more) layers are stacked, an electric charge generation layer 320 ais preferably provided between an m-th EL layer 320 and an (m+1)th ELlayer 320. Note that in is a natural number greater than or equal to 1and less than n. The components other than the electrode 318 and theelectrode 322 correspond to the EL layer 117 of the aforementionedEmbodiments.

The electric charge generation layer 320 a can be formed using acomposite material of an organic compound and a metal oxide. Examples ofthe metal oxide are vanadium oxide, molybdenum oxide, tungsten oxide, orthe like. As the organic compound, a variety of compounds can be used;for example, an aromatic amine compound, a carbazole derivative, anaromatic hydrocarbon, and an oligomer, a dendrimer, and a polymer havinga basic skeleton of these compounds can be used. Note that as theorganic compound, it is preferable to use an organic compound that has ahole-transport property and has a hole mobility of 10⁻⁶ cm²/Vs orhigher. However, other substances may be used as long as theirhole-transport properties are higher than their electron-transportproperties. These materials used for the electric charge generationlayer 320 a have excellent carrier-injection properties andcarrier-transport properties; thus, the light-emitting element 331 canbe driven with low current and with low voltage. Other than thecomposite material, the metal oxide, a composite material of an organiccompound and an alkali metal, an alkaline earth metal, or a compound ofthe alkali metal or the alkaline earth metal can be used in the electriccharge generation layer 320 a.

Note that the electric charge generation layer 320 a may be formed by acombination of a composite material of an organic compound and a metaloxide with another material. For example, the electric charge generationlayer 320 a may be formed by a combination of a layer containing thecomposite material of an organic compound and a metal oxide with a layercontaining one compound selected from electron-donating substances and acompound having a high electron-transport property. Furthermore, theelectric charge generation layer 320 a may be formed by a combination ofa layer containing the composite material of an organic compound and ametal oxide with a transparent conductive film.

The light-emitting element 331 having such a structure is unlikely toresult in energy transfer between the neighboring EL layer 320 and caneasily realize high emission efficiency and a long lifetime.Furthermore, it is easy to obtain phosphorescence from onelight-emitting layer and fluorescence from the other light-emittinglayer.

The electric charge generation layer 320 a has a function of injectingholes to one of the EL layers 320 that is in contact with the electriccharge generation layer 320 a and a function of injecting electrons tothe other EL layer 320 that is in contact with the electric chargegeneration layer 320 a, when voltage is applied to the electrodes 318and 322.

The light-emitting element 331 illustrated in FIG. 20B can provide avariety of emission colors by changing the type of the light-emittingsubstance used for the EL layers 320. In addition, a plurality oflight-emitting substances having different emission colors may be usedas the light-emitting substances, so that light emission having a broadspectrum or white light emission can be obtained.

In the case of obtaining white light emission using the light-emittingelement 331 in FIG. 20B, as for a combination of a plurality of ELlayers, a structure for emitting white light including red light, bluelight, and green light may be used. For example, the structure mayinclude an EL layer containing a blue fluorescent substance as alight-emitting substance and an EL layer containing green and redphosphorescent substances as light-emitting substances. Alternatively,the structure may include an EL layer emitting red light, an EL layeremitting green light, and an EL layer emitting blue light. Furtheralternatively, with a structure including EL layers emitting light ofcomplementary colors, white light emission can be obtained. In astacked-layer element including two EL layers which emit lights withcomplementary colors, the combinations of colors are as follows: blueand yellow, blue-green and red, and the like.

Note that in the structure of the above stacked-layer element, byproviding the electric charge generation layer between the stackedlight-emitting layers, the element can give a high-luminance region at alow current density, and have a long lifetime.

This embodiment can be implemented in an appropriate combination withany of the structures described in the other embodiments.

Embodiment 6

In this embodiment, a display module using the display device of oneembodiment of the present invention will be described with reference toFIG. 21.

In a display module 8000 illustrated in FIG. 21, a touch sensor 8004connected to an FPC 8003, a cell 8006 connected to an FPC 8005, abacklight unit 8007, a frame 8009, a printed board 8010, and a battery8011 are provided between an upper cover 8001 and a lower cover 8002. Atleast one of the upper cover 8001, the lower cover 8002, the backlightunit 8007, the frame 8009, the printed board 8010, the battery 8011, thetouch sensor 8004, and the like is not provided in some cases.

The display device of one embodiment of the present invention can beused for the cell 8006, for example.

The shapes and sizes of the upper cover 8001 and the lower cover 8002can be changed as appropriate in accordance with the sizes of the touchsensor 8004 and the cell 8006.

The touch sensor 8004 can be a resistive touch sensor or a capacitivetouch sensor and may be formed to overlap with the cell 8006. A countersubstrate (sealing substrate) of the cell 8006 can have a touch sensorfunction. A photosensor may be provided in each pixel of the cell 8006so that an optical touch sensor is obtained. An electrode for a touchsensor may be provided in each pixel of the cell 8006 so that acapacitive touch sensor is obtained.

The backlight unit 8007 includes a light source 8008. The light source8008 may be provided at an end portion of the backlight unit 8007 and alight diffusing plate may be used. In the case where a display deviceincluding a light-emitting element and the like is used for the cell8006, the backlight unit 8007 is not necessarily provided.

The frame 8009 may protect the cell 8006 and also function as anelectromagnetic shield for blocking electromagnetic waves generated bythe operation of the printed board 8010. The frame 8009 may function asa radiator plate.

The printed board 8010 has a power supply circuit and a signalprocessing circuit for outputting a video signal and a clock signal. Asa power source for supplying power to the power supply circuit, anexternal power source or a power source using the battery 8011 providedseparately may be used. The battery 8011 can be omitted in the case ofusing an external power source.

The display module 8000 can be additionally provided with a member suchas a polarizing plate, a retardation plate, or a prism sheet.

This embodiment can be implemented in an appropriate combination withany of the structures described in the other embodiments.

Embodiment 7

In this embodiment, examples of an electronic device and a lightingdevice including the display device of one embodiment of the presentinvention will be described with reference to drawings.

Specific examples of the electronic device that uses the display deviceof one embodiment of the present invention are as follows: displaydevices of televisions, monitors, and the like, lighting devices,desktop and laptop personal computers, word processors, imagereproduction devices which reproduce still images and moving imagesstored in recording media such as digital versatile discs (DVDs),portable CD players, radios, tape recorders, headphone stereos, stereos,table clocks, wall clocks, cordless phone handsets, transceivers, mobilephones, car phones, portable game machines, tablet terminals, large gamemachines such as pachinko machines, calculators, portable informationterminals, electronic notebooks, e-book readers, electronic translators,audio input devices, video cameras, digital still cameras, electricshavers, high-frequency heating appliances such as microwave ovens,electric rice cookers, electric washing machines, electric vacuumcleaners, water heaters, electric fans, hair dryers, air-conditioningsystems such as air conditioners, humidifiers, and dehumidifiers,dishwashers, dish dryers, clothes dryers, futon dryers, electricrefrigerators, electric freezers, electric refrigerator-freezers,freezers for preserving DNA, flashlights, electrical tools such as achain saw, smoke detectors, and medical equipment such as dialyzers.Other examples are as follows: industrial equipment such as guidelights, traffic lights, conveyor belts, elevators, escalators,industrial robots, power storage systems, and power storage devices forleveling the amount of power supply and smart grid. In addition, movingobjects and the like driven by electric motors using power from a powerstorage unit are also included in the category of electronic devices.Examples of the moving objects include electric vehicles (EV), hybridelectric vehicles (HEV) which include both an internal-combustion engineand a motor, plug-in hybrid electric vehicles (PHEV), tracked vehiclesin which caterpillar tracks are substituted for wheels of thesevehicles, motorized bicycles including motor-assisted bicycles,motorcycles, electric wheelchairs, golf carts, boats, ships, submarines,helicopters, aircrafts, rockets, artificial satellites, space probes,planetary probes, and spacecrafts.

In particular, as examples of electronic devices including a displaydevice with flexibility, the following can be given: television devices(also referred to as televisions or television receivers), monitors ofcomputers or the like, digital cameras, digital video cameras, digitalphoto frames, mobile phones (also referred to as cellular phones ormobile phone devices), portable game machines, portable informationterminals, audio reproducing devices, large game machines such aspachinko machines, and the like.

In addition, a lighting device or a display device can be incorporatedalong a curved inside/outside wall surface of a house or a building or acurved interior/exterior surface of a car.

FIG. 22A is an example of a mobile phone. A mobile phone 7400 includes adisplay portion 7402 that is incorporated in a housing 7401. The mobilephone 7400 further includes operation buttons 7403, an externalconnection port 7404, a speaker 7405, a microphone 7406, and the like.The mobile phone 7400 is manufactured using the display device for thedisplay portion 7402.

When the display portion 7402 is touched with a finger or the like, datacan be input into the mobile phone 7400 in FIG. 22A. Furthermore,operations such as making a call and inputting a letter can be performedby touch on the display portion 7402 with a finger or the like.

With the operation buttons 7403, power ON/OFF can be switched. Inaddition, types of images displayed on the display portion 7402 can beswitched; for example, switching images from a mail creation screen to amain menu screen.

Here, the display portion 7402 includes the display device of oneembodiment of the present invention. Thus, the mobile phone can have acurved display portion and high reliability.

FIG. 22B is an example of a wristband-type display device. A portabledisplay device 7100 includes a housing 7101, a display portion 7102,operation buttons 7103, and a transceiver 7104.

The portable display device 7100 can receive a video signal with thetransceiver 7104 and can display the received video on the displayportion 7102. In addition, with the transceiver 7104, the portabledisplay device 7100 can send an audio signal to another receivingdevice.

With the operation button 7103, power ON/OFF, switching displayedvideos, adjusting volume, and the like can be performed.

Here, the display portion 7102 includes the display device of oneembodiment of the present invention. Thus, the portable display devicecan have a curved display portion and high reliability.

FIGS. 22C to 22E show examples of lighting devices. Lighting devices7200, 7210, and 7220 each include a stage 7201 provided with anoperation switch 7203 and a light-emitting portion supported by thestage 7201.

The lighting device 7200 illustrated in FIG. 22C includes alight-emitting portion 7202 with a wave-shaped light-emitting surfaceand thus is a good-design lighting device.

A light-emitting portion 7212 included in the lighting device 7210illustrated in FIG. 22D has two convex-curved light-emitting portionssymmetrically placed. Thus, light radiates from the lighting device 7210in all directions.

The lighting device 7220 illustrated in FIG. 22E includes aconcave-curved light-emitting portion 7222. This is suitable forilluminating a specific range because light emitted from thelight-emitting portion 7222 is collected to the front of the lightingdevice 7220.

The light-emitting portion included in each of the lighting devices7200, 7210, and 7220 is flexible; thus, the light-emitting portion canbe fixed on a plastic member, a movable frame, or the like so that anemission surface of the light-emitting portion can be curved freelydepending on the intended use.

The light-emitting portions included in the lighting devices 7200, 7210,and 7220 each include the display device of one embodiment of thepresent invention. Thus, the light-emitting portions can be curved orbent into any shape and the lighting devices can have high reliability.

FIG. 23A shows an example of a portable display device. A display device7300 includes a housing 7301, a display portion 7302, operation buttons7303, a display portion pull 7304, and a control portion 7305.

The display device 7300 includes the rolled flexible display portion7302 in the cylindrical housing 7301.

The display device 7300 can receive a video signal with the controlportion 7305 and can display the received video on the display portion7302. In addition, a power storage device is included in the controlportion 7305. Moreover, a connector may be included in the controlportion 7305 so that a video signal or power can be supplied directly.

With the operation buttons 7303, power ON/OFF, switching of displayedvideos, and the like can be performed.

FIG. 23B illustrates a state where the display portion 7302 is pulledout with the display portion pull 7304. Videos can be displayed on thedisplay portion 7302 in this state. Furthermore, the operation buttons7303 on the surface of the housing 7301 allow one-handed operation.

Note that a reinforcement frame may be provided for an edge portion ofthe display portion 7302 in order to prevent the display portion 7302from being curved when pulled out.

Note that in addition to this structure, a speaker may be provided forthe housing so that sound is output with an audio signal receivedtogether with a video signal.

The display portion 7302 includes the display device of one embodimentof the present invention. Thus, the display portion 7302 is a displaydevice which is flexible and highly reliable, which makes the displaydevice 7300 lightweight and highly reliable.

FIGS. 24A and 24B show a double foldable tablet terminal 9600 as anexample. FIG. 24A illustrates the tablet terminal 9600 which isunfolded. The tablet terminal 9600 includes a housing 9630, a displayportion 9631, a display mode switch 9626, a power switch 9627, apower-saving mode switch 9625, a clasp 9629, and an operation switch9628.

The housing 9630 includes a housing 9630 a and a housing 9630 b, whichare connected with a hinge portion 9639. The hinge portion 9639 makesthe housing 9630 double foldable.

The display portion 9631 is provided on the housing 9630 a, the housing9630 b, and the hinge portion 9639. By the use of the display devicedisclosed in this specification and the like for the display portion9631, the tablet terminal in which the display portion 9631 is foldableand which has high reliability can be provided.

Part of the display portion 9631 can be a touchscreen region 9632 anddata can be input when a displayed operation key 9638 is touched. Astructure can be employed in which half of the display portion 9631 hasonly a display function and the other half has a touchscreen function.The whole display portion 9631 may have a touchscreen function. Forexample, keyboard buttons may be displayed on the entire region of thedisplay portion 9631 so that the display portion 9631 can be used as adata input terminal.

The display mode switch 9626 can switch the display between a portraitmode and a landscape mode, and between monochrome display and colordisplay, for example. The power-saving mode switch 9625 can controldisplay luminance in accordance with the amount of external light in useof the tablet terminal detected by an optical sensor incorporated in thetablet terminal. Another detection device including a sensor fordetecting inclination, such as a gyroscope or an acceleration sensor,may be incorporated in the tablet terminal, in addition to the opticalsensor.

FIG. 24B illustrates the tablet terminal 9600 which is folded. Thetablet terminal 9600 includes the housing 9630, a solar cell 9633, and acharge and discharge control circuit 9634. As an example, FIG. 24Billustrates the charge and discharge control circuit 9634 including abattery 9635 and a DC-to-DC converter 9636.

By including the display device that is disclosed in this specificationand the like, the display portion 9631 is foldable. Since the tabletterminal 9600 is double foldable, the housing 9630 can be closed whenthe tablet terminal is not in use, for example; thus, the tabletterminal is highly portable. Moreover, since the display portion 9631can be protected when the housing 9630 is closed, the tablet terminalcan have high durability and high reliability for long-term use.

The tablet terminal illustrated in FIGS. 24A and 24B can have otherfunctions such as a function of displaying various kinds of data (e.g.,a still image, a moving image, and a text image), a function ofdisplaying a calendar, a date, the time, or the like on the displayportion, a touch-input function of operating or editing the datadisplayed on the display portion by touch input, and a function ofcontrolling processing by various kinds of software (programs).

The solar cell 9633 provided on a surface of the tablet terminal cansupply power to the touch sensor, the display portion, a video signalprocessing portion, or the like. Note that the solar cell 9633 ispreferably provided on one or both surfaces of the housing 9630, inwhich case the battery 9635 can be charged efficiently. When a lithiumion battery is used as the battery 9635, there is an advantage ofdownsizing or the like.

The structure and operation of the charge and discharge control circuit9634 illustrated in FIG. 24B is described with reference to a blockdiagram of FIG. 24C. FIG. 24C illustrates the solar cell 9633, thebattery 9635, the DC-to-DC converter 9636, a converter 9637, switchesSW1 to SW3, and the display portion 9631. The battery 9635, the DC-to-DCconverter 9636, the converter 9637, and the switches SW1 to SW3correspond to the charge and discharge control circuit 9634 illustratedin FIG. 24B.

First, description is made on an example of the operation in the casewhere power is generated by the solar cell 9633 with the use of externallight. The voltage of the power generated by the solar cell is raised orlowered by the DC-to-DC converter 9636 so as to be voltage for chargingthe battery 9635. Then, when power from the solar cell 9633 is used forthe operation of the display portion 9631, the switch SW1 is turned onand the voltage of the power is raised or lowered by the converter 9637so as to be voltage needed for the display portion 9631. When images arenot displayed on the display portion 9631, the switch SW1 is turned offand the switch SW2 is turned on so that the battery 9635 is charged.

Although the solar cell 9633 is described as an example of a powergeneration unit, the power generation unit is not particularly limited,and the battery 9635 may be charged by another power generation unitsuch as a piezoelectric element or a thermoelectric conversion element(Peltier element). For example, the battery 9635 may be charged using anon-contact power transmission module that transmits and receives powerwirelessly (without contact) or using another charge unit incombination.

An electronic device 7700 illustrated in FIGS. 25A to 25C and FIGS. 26Aand 26B has the display portion 7702 including the foldable displaydevice disclosed in the above embodiments. FIG. 25A is a plan viewshowing a state where the display portion 7702 is unfolded. Across-sectional view of the electronic device 7700 is illustrated inFIG. 25B. A power storage device 7704 is provided inside the electronicdevice 7700. FIG. 26A corresponds to an external perspective viewshowing a state where the display portion 7702 is unfolded.

Furthermore, hinges 7701 and 7703 that allow the display portion 7702 tobe folded are provided. The display portion 7702 is an active matrixdisplay device including an organic EL element over a plastic substrateand is a flexible display panel. For example, a transistor having anoxide semiconductor layer is included, the transistor and the organic ELelement are electrically connected to each other, and the transistor andthe organic EL element are placed between two plastic substrates. Theelectronic device illustrated in FIGS. 25A to 25C and FIGS. 26A and 26Bis an example of the electronic device 7700 which can be reduced in sizeby folding at portions where the hinges 7701 and 7703 are provided.

FIG. 25C is a cross-sectional view of the electronic device in a foldedstate. FIG. 26B corresponds to an external perspective view of theelectronic device in the state. The example of folding two places usingthe two hinges 7701 and 7703 is given; however, folding of theelectronic device is not limited thereto. An electronic device which canbe folded at three or more places may be obtained by increasing the sizeof the display portion 7702 and the number of hinges. Alternatively, anelectronic device which can be folded at one place using one hinge maybe obtained.

By selecting a material (a silicone rubber or a plastic material) of thehousing of the electronic device 7700 so that a flexible housing isobtained, the electronic device 7700 can be folded wholly or partlywhile a foldable power storage device is used for the power storagedevice 7704 provided inside the housing. According to one embodiment ofthe present invention, an electronic device with high portability can beprovided.

It is needless to say that one embodiment of the present invention isnot limited to the above-described electronic devices and lightingdevices as long as the display device of one embodiment of the presentinvention is included.

This embodiment can be implemented in an appropriate combination withany of the structures described in the other embodiments.

Note that content (or may be part of the content) described in oneembodiment may be applied to, combined with, or replaced by differentcontent (or may be part of the different content) described in theembodiment and/or content (or may be part of the content) described inone or more different embodiments.

Note that in each embodiment, content described in the embodiment iscontent described with reference to a variety of diagrams or contentdescribed with a text described in the specification.

Note that by combining a diagram (or may be part of the diagram)illustrated in one embodiment with another part of the diagram, adifferent diagram (or may be part of the different diagram) illustratedin the embodiment, and/or a diagram (or may be part of the diagram)illustrated in another embodiment or other embodiments, much morediagrams can be formed.

Note that content that is not specified in any drawing or text in thespecification can be excluded from one embodiment of the invention.Alternatively, when the range of a value that is defined by the maximumand minimum values is described, part of the range is approximatelynarrowed or part of the range is removed, whereby one embodiment of theinvention excluding part of the range can be constituted. In thismanner, it is possible to specify the technical scope of one embodimentof the present invention so that a conventional technology is excluded,for example.

As a specific example, a diagram of a circuit including first to fifthtransistors is illustrated. In that case, it can be specified that thecircuit does not include a sixth transistor in the invention. It can bespecified that the circuit does not include a capacitor in theinvention. It can be specified that the circuit does not include a sixthtransistor with a particular connection in the invention. It can bespecified that the circuit does not include a capacitor with aparticular connection in the invention. For example, it can be specifiedthat a sixth transistor whose gate is connected to a gate of the thirdtransistor is not included in the invention. It can be specified that acapacitor whose first electrode is connected to the gate of the thirdtransistor is not included in the invention, for example.

As another specific example, when the expression “voltage is preferablyhigher than or equal to 3 V and lower than or equal to 10 V” is used todescribe a given value, for example, it can be specified that the casewhere the voltage is higher than or equal to −2 V and lower than orequal to 1 V is excluded from one embodiment of the invention. Forexample, it can be specified that the case where the voltage is higherthan or equal to 13 V is excluded from one embodiment of the invention.Note that, for example, it can be specified that the voltage is higherthan or equal to 5 V and lower than or equal to 8 V in the invention.For example, it can be specified that the voltage is approximately 9 Vin the invention. For example, it can be specified that the voltage ishigher than or equal to 3 V and lower than or equal to 10 V but not 9 Vin the invention. Note that even when the expression “a value ispreferably in a certain range” or “a value preferably satisfies acertain condition” is used, for example, the value is not limited to thedescription. In other words, the description of a value that includes aterm “preferable”, “preferably”, or the like does not necessarily limitthe value.

As another specific example, when the expression “voltage is preferably10 V” is used to describe a given value, for example, it can bespecified that the case where the voltage is higher than or equal to −2V and lower than or equal to 1 V is excluded from one embodiment of theinvention. For example, it can be specified that the case where thevoltage is higher than or equal to 13 V is excluded from one embodimentof the invention.

As another specific example, when the expression “a film is aninsulating film” is used to describe properties of a material, forexample, it can be specified that the case where the insulating film isan organic insulating film is excluded from one embodiment of theinvention. For example, it can be specified that the case where theinsulating film is an inorganic insulating film is excluded from oneembodiment of the invention. For example, it can be specified that thecase where the insulating film is a conductive film is excluded from oneembodiment of the invention. For example, it can be specified that thecase where the insulating film is a semiconductor film is excluded fromone embodiment of the invention.

As another specific example, when the expression “a film is providedbetween an A film and a B film” is used to describe a given layeredstructure, for example, it can be specified that the case where the filmis a stacked film of four or more layers is excluded from the invention.For example, it can be specified that the case where a conductive filmis provided between the A film and the film is excluded from theinvention.

Note that various people can implement one embodiment of the inventiondescribed in this specification and the like. However, different peoplemay be involved in the implementation of the embodiment of theinvention. For example, in the case of a transmission/reception system,the following case is possible: Company A manufactures and sellstransmitting devices, and Company B manufactures and sells receivingdevices. As another example, in the case of a light-emitting deviceincluding a transistor and a light-emitting element, the following caseis possible: Company A manufactures and sells semiconductor devicesincluding transistors, and Company B purchases the semiconductordevices, provides light-emitting elements for the semiconductor devices,and completes light-emitting devices.

In such a case, one embodiment of the invention can be constituted sothat a patent infringement can be claimed against each of Company A andCompany B. In other words, one embodiment of the invention can beconstituted so that only Company A implements the embodiment, andanother embodiment of the invention can be constituted so that onlyCompany B implements the embodiment. One embodiment of the inventionwith which a patent infringement suit can be filed against Company A orCompany B is clear and can be regarded as being disclosed in thisspecification or the like. For example, in the case of atransmission/reception system, even when this specification or the likedoes not include a description of the case where a transmitting deviceis used alone or the case where a receiving device is used alone, oneembodiment of the invention can be constituted by only the transmittingdevice and another embodiment of the invention can be constituted byonly the receiving device. Those embodiments of the invention are clearand can be regarded as being disclosed in this specification or thelike. Another example is as follows: in the case of a light-emittingdevice including a transistor and a light-emitting element, even whenthis specification or the like does not include a description of thecase where a semiconductor device including the transistor is used aloneor the case where a light-emitting device including the light-emittingelement is used alone, one embodiment of the invention can beconstituted by only the semiconductor device including the transistorand another embodiment of the invention can be constituted by only thelight-emitting device including the light-emitting element. Thoseembodiments of the invention are clear and can be regarded as beingdisclosed in this specification or the like.

Note that in this specification and the like, it may be possible forthose skilled in the art to constitute one embodiment of the inventioneven when portions to which all the terminals of an active element(e.g., a transistor or a diode), a passive element (e.g., a capacitor ora resistor), and the like are connected are not specified. In otherwords, one embodiment of the invention is clear even when connectionportions are not specified. Furthermore, in the case where a connectionportion is disclosed in this specification and the like, it can bedetermined that one embodiment of the invention in which a connectionportion is not specified is disclosed in this specification and thelike, in some cases. In particular, in the case where the number ofportions to which the terminal is connected may be more than one, it isnot necessary to specify the portions to which the terminal isconnected. Therefore, it may be possible to constitute one embodiment ofthe invention by specifying only portions to which some of terminals ofan active element (e.g., a transistor or a diode), a passive element(e.g., a capacitor or a resistor), and the like are connected.

Note that in this specification and the like, it may be possible forthose skilled in the art to specify the invention when at least theconnection portion of a circuit is specified. Alternatively, it may bepossible for those skilled in the art to specify the invention when atleast a function of a circuit is specified. In other words, when afunction of a circuit is specified, one embodiment of the presentinvention is clear. Moreover, it can be determined that one embodimentof the present invention whose function is specified is disclosed inthis specification and the like. Therefore, when a connection portion ofa circuit is specified, the circuit is disclosed as one embodiment ofthe invention even when a function is not specified, and one embodimentof the invention can be constituted. Alternatively, when a function of acircuit is specified, the circuit is disclosed as one embodiment of theinvention even when a connection portion is not specified, and oneembodiment of the invention can be constituted.

Note that in this specification and the like, part of a diagram or textdescribed in one embodiment can be taken out to constitute oneembodiment of the invention. Thus, in the case where a diagram or textrelated to a certain portion is described, the contents taken out frompart of the diagram or the text are also disclosed as one embodiment ofthe invention, and one embodiment of the invention can be constituted.The embodiment of the present invention is clear. Therefore, forexample, in a diagram or text in which one or more active elements(e.g., transistors or diodes), wirings, passive elements (e.g.,capacitors or resistors), conductive layers, insulating layers,semiconductor layers, organic materials, inorganic materials,components, devices, operating methods, manufacturing methods, or thelike are described, part of the diagram or the text is taken out, andone embodiment of the invention can be constituted. For example, from acircuit diagram in which N circuit elements (e.g., transistors orcapacitors; N is an integer) are provided, it is possible to take out Mcircuit elements (e.g., transistors or capacitors; M is an integer,where M<N) and constitute one embodiment of the invention. For anotherexample, it is possible to take out M layers (M is an integer, whereM<N) from a cross-sectional view in which N layers (N is an integer) areprovided and constitute one embodiment of the invention. For anotherexample, it is possible to take out M elements (M is an integer, whereM<N) from a flow chart in which N elements (N is an integer) areprovided and constitute one embodiment of the invention. For anotherexample, it is possible to take out some given elements from a sentence“A includes B, C, D, E, or F” and constitute one embodiment of theinvention, for example, “A includes B and E”, “A includes E and F”, “Aincludes C, E, and F”, or “A includes B, C, D, and E”.

Note that in the case where at least one specific example is describedin a diagram or text described in one embodiment in this specificationand the like, it will be readily appreciated by those skilled in the artthat a broader concept of the specific example can be derived.Therefore, in the diagram or the text described in one embodiment, inthe case where at least one specific example is described, a broaderconcept of the specific example is disclosed as one embodiment of theinvention, and one embodiment of the invention can be constituted. Theembodiment of the present invention is clear.

Note that in this specification and the like, what is illustrated in atleast a diagram (which may be part of the diagram) is disclosed as oneembodiment of the invention, and one embodiment of the invention can beconstituted. Therefore, when certain contents are described in adiagram, the contents are disclosed as one embodiment of the inventioneven when the contents are not described with text, and one embodimentof the invention can be constituted. In a similar manner, part of adiagram, which is taken out from the diagram, is disclosed as oneembodiment of the invention, and one embodiment of the invention can beconstituted. The embodiment of the present invention is clear.

This application is based on Japanese Patent Application serial no.2014-050438 filed with Japan Patent Office on Mar. 13, 2014, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. An electronic device comprising: a first flexiblesubstrate; an electrode over the first flexible substrate; a firstinsulating layer over the electrode; a first bonding layer over thefirst insulating layer; a second insulating layer over the first bondinglayer; a second bonding layer over the second insulating layer; a secondflexible substrate over the second bonding layer; and a conductiveconnection layer in contact with the electrode through a first openingopened in the first insulating layer and in the first bonding layer, anda second opening opened in the second flexible substrate, wherein thesecond bonding layer is in contact with a side surface of the conductiveconnection layer and a side surface of the first bonding layer.
 2. Theelectronic device according to claim 1, wherein the conductiveconnection layer is an anisotropic conductive film or an anisotropicconductive paste.
 3. The electronic device according to claim 1, furthercomprising a flexible printed circuit in contact with the conductiveconnection layer.
 4. The electronic device according to claim 1, furthercomprising a light-emitting element between the first insulating layerand the first bonding layer.
 5. The electronic device according to claim1, wherein the electronic device is one selected from the groupconsisting of a mobile phone, a wristband-type display device, alighting device, and a tablet terminal.
 6. An electronic devicecomprising: a first flexible substrate; an electrode over the firstflexible substrate; a first insulating layer over the electrode; a firstbonding layer over the first insulating layer; a second insulating layerover the first bonding layer; a second bonding layer over the secondinsulating layer; a second flexible substrate over the second bondinglayer; and a conductive connection layer in contact with the electrodethrough a first opening opened in the first insulating layer and in thefirst bonding layer, and a second opening opened in the second flexiblesubstrate, wherein the second bonding layer is in contact with a sidesurface of the conductive connection layer and a side surface of thefirst bonding layer, and wherein a width of the second opening issmaller than a width of the first opening.
 7. The electronic deviceaccording to claim 6, wherein the conductive connection layer is ananisotropic conductive film or an anisotropic conductive paste.
 8. Theelectronic device according to claim 6, further comprising a flexibleprinted circuit in contact with the conductive connection layer.
 9. Theelectronic device according to claim 6, further comprising alight-emitting element between the first insulating layer and the firstbonding layer.
 10. The electronic device according to claim 6, whereinthe electronic device is one selected from the group consisting of amobile phone, a wristband-type display device, a lighting device, and atablet terminal.